Alloys doi: 10.3390/alloys5020010

Authors: Mihail Kolev

This study presents a comprehensive bibliometric analysis of research on 2xxx series aluminum–copper (Al–Cu) alloys published between 2020 and 2025. A complete analysis of 4380 documents from 747 sources indexed in Scopus reveals sustained research growth, with publications rising from 603 in 2020 to 948 in 2025 at a compound annual growth rate of 9.5%. China dominates global output, contributing 35.7% of publications with Central South University as the leading institution (548 articles). However, China’s international collaboration rate (12.2%) remains notably lower than Western counterparts such as the United Kingdom (62.5%) and Canada (53.2%). Core journals including the Journal of Alloys and Compounds, Materials Science and Engineering: A, and Journal of Materials Research and Technology collectively account for 11.4% of total publications, conforming to Bradford’s Law concentration patterns. Keyword co-occurrence analysis revealed five distinct thematic clusters centered on microstructure–property relationships, friction stir welding and joining technologies, corrosion mechanisms, Al–Cu–Li aerospace alloys, and additive manufacturing. While life cycle modeling (K = 5993; tm = 2022.84) indicates the field is approaching maturity, by identifying emerging frontiers such as machine learning-assisted alloy design, sustainable processing routes, and multi-material joining for electric vehicles, this study offers researchers a quantitative roadmap of the Al–Cu alloy knowledge landscape and highlights strategic opportunities for future investigation.

Alloys doi: 10.3390/alloys5020009

Authors: Mihail Kolev

The development of high-performance copper alloys requires balancing mechanical strength and electrical conductivity, properties that are often inversely correlated due to competing strengthening mechanisms. This study presents a comparative machine learning analysis of Cu-Ni-Si and Cu low alloys using a curated dataset of 1690 entries derived from the Gorsse et al. database, comprising 1507 samples with hardness measurements and 1685 samples with electrical conductivity data. Three ensemble-based regression algorithms, Random Forest, XGBoost, and Gradient Boosting, were trained to predict Vickers hardness (HV) and electrical conductivity (%IACS) from an augmented feature set encompassing alloy composition, thermomechanical processing parameters, missingness indicators, and physics-informed descriptors (valence electron concentration, atomic size mismatch, electronegativity difference, and Ni:Si atomic ratio). XGBoost achieved optimal performance for hardness prediction (R2 = 0.8554, RMSE = 29.90 HV), while Gradient Boosting performed best for electrical conductivity (R2 = 0.8400, RMSE = 5.96%IACS). Averaged tree-based feature-importance analysis identified valence electron concentration as the most influential predictor for hardness (39.9%), followed by aging temperature (11.2%), while Cu content dominated conductivity prediction (37.7%), followed by aging time (8.9%). Complementary SHAP analysis confirmed these trends while revealing directional relationships and nonlinear feature interaction effects. Composition-grouped cross-validation by unique alloy formula (K = 10) yielded substantially lower performance, with grouped CV R2 = 0.438 for hardness and 0.293 for conductivity, indicating that generalization to unseen alloy formulations remains limited. The models were further applied for practical tasks, including property prediction for new alloy compositions, processing parameter optimization via differential evolution with metallurgical constraints (achieving hardness up to 293.9 HV or conductivity up to 45.7%IACS for the same base composition, with prediction intervals reported), and inverse design to identify alloy formulations meeting specified target properties. This work demonstrates the potential of interpretable machine learning to support copper alloy development by enabling rapid computational screening of the compositional and processing parameter space, subject to the generalization limitations identified herein.

Alloys doi: 10.3390/alloys5010008

Authors: Mihail Kolev Vladimir Petkov Rumyana Lazarova Veselin Petkov Krasimir Kolev Shaban Uzun

Cr-based composite coatings with superior wear resistance are in growing demand for high-performance applications in the automotive, aerospace, and general manufacturing sectors. In this study, an Al10Cu alloy produced via powder metallurgy was coated with a chromium/nanodiamond (Cr/ND) composite layer using an electrodeposition process to enhance its tribological performance. The coatings were characterized using scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray diffraction. The resulting Cr/ND layer exhibited a uniform thickness of 73.5–76.2 μm and markedly improved surface hardness (809.4 HV), representing a 15-fold increase over the uncoated alloy (53.6 HV). Pin-on-disk tribological testing under dry sliding conditions showed complete elimination of detectable mass loss (0.00 mg vs. 0.55 mg for uncoated) within the measurement system resolution, indicating excellent resistance to both abrasive and adhesive wear. XRD analysis revealed the formation of a hexagonal close-packed Cr2H phase with incorporated nanodiamond particles. To capture and predict the temporal evolution of the friction coefficient, a customized dual-layer long short-term memory neural network—optimized with a look-back window of 3 timesteps and ReLU-activated dense layers—was implemented. The model achieved superior predictive performance on the coated system, with validation and test R2 values of 0.9973 and 0.9965, respectively, demonstrating enhanced modeling accuracy for surface-engineered materials. These findings demonstrate a significant advancement in wear protection for aluminum alloys and introduce a robust data-driven approach for real-time friction prediction in engineered surfaces.

Alloys doi: 10.3390/alloys5010007

Authors: Shamim Pourrahimi Soroosh Hakimian

Machine learning (ML) is becoming an established part of alloy research, offering new ways to link composition, processing routes, and microstructure with measured properties. In this work, recent studies using ML for predicting or optimizing alloy behavior are reviewed, covering mechanical, corrosion, phase-related, and physical properties. Unlike previous reviews organized by alloy system or modeling approach, this review is structured by target property (mechanical, corrosion, phase/structure, and physical), which helps identify the input features commonly used to model each property and highlights existing gaps in data and validation. For each study, the main property of interest, dataset features, model type, algorithm choice, use of hyperparameter tuning, and validation strategy were examined. Comparing these reports shows that ensemble models such as random forest and XGBoost, together with deep neural networks, usually perform better than linear approaches. At the same time, issues related to small datasets and inconsistent reporting remain major challenges. Attention is also drawn to new directions, particularly physics-based learning and multi-objective optimization, that are changing how ML is applied in materials design. Overall, this review summarizes current practices and outlines areas where closer integration of data-driven and experimental methods could accelerate the development of next-generation alloys.

Alloys doi: 10.3390/alloys5010006

Authors: Y. Upadhyaya Afham Ahmad Vishwanath Managuli

Damage is a phenomenon experienced when a material is subjected to external factors such as load and temperature. Damage is quantified through the damage value of a material, and its value typically ranges from 0 to 1, with 1 indicating complete damage. The damage value in this context primarily refers to the crack initiation condition, indicating failure. The damage value corresponding to this condition is referred to as critical damage. However, most materials tend to fail at a critical damage value of less than one. Researchers have developed different models to evaluate damage, and some of the prominent models are Lemaitre, Rice & Tracy, Gurson, and Bhattacharya & Ellingwood. This study uses the Bhattacharya & Ellingwood model to evaluate the damage value of 113 selected steel materials that play crucial roles in aerospace, automobile, and other industrial applications. This model uses monotonic properties of the material as the input and estimates the critical damage value (Dc). The study revealed that, for steel materials, the Dc value generally ranges from 0.1 to 0.7. This study highlights the variation in damage with plastic strain under monotonic loading, and this helps to quickly select a specific material when the damage criterion is crack initiation.

Alloys doi: 10.3390/alloys5010005

Authors: Weiran Xie Xiaoming Duan Xiaodong Yang

In metal additive manufacturing, the molten pool directly influences the performance of the fabricated components. Therefore, a comprehensive understanding of the molten pool behavior is essential for improving the quality of the parts and mitigating the formation of defects. Selective arc melting (SAM) is a promising additive manufacturing method for fabricating metal matrix composites. However, the melting and solidification process of the powder layer under the arc heat source remains unrevealed. This study aims to elucidate the formation mechanisms of surface morphology during SAM processing and the influence of carbide addition on the melting and solidification behavior of Inconel 718 powder. In this study, thin-walled parts of Inconel 718 and TiC/Inconel 718 composite were fabricated and their microstructures were studied. The melting and solidification behavior of Inconel 718 and TiC/Inconel 718 composite during single-track single-layer deposition was investigated using high-speed photography. Focusing on the differences in the sidewall surface morphology of the Inconel 718 and TiC/Inconel 718 composite parts, the edge feature formation of the deposition track of both materials was studied. Furthermore, the formation mechanism of the differences in forming height at different positions of the deposition track was explored. The results indicate that the melted material in the molten pool of Inconel 718 mainly comes from the mass transport of the beads generated around the molten pool, while the liquid material in the molten pool of TiC/Inconel 718 composite mainly comes from the in situ powder melted under the arc center. During the melting process of Inconel 718 powder, beads at the edge of the heating area come into contact with the boundary of the molten pool and solidify in situ, forming protrusion features. The randomness in the bead size leads to different volumes of molten material at different positions within the same time, thereby causing variations in building height.

Alloys doi: 10.3390/alloys5010004

Authors: Luiza Emília Vila Nova Mazzoni Fernanda Mariano Pereira Estefani Alves da Silva Calabria Luca de Paulo Ferreira Alfredo Rocha de Faria Tamires de Souza Nossa Kahl Dick Zilnyk

This study provides the first complete and experimentally validated Yoshida–Uemori (Y–U) parameter set for AA6005C aluminum alloy, enabling accurate constitutive modeling for stamping simulations. A comprehensive set of mechanical tests was conducted, comprising uniaxial tensile tests along 0°, 45°, and 90° to the rolling direction, hydraulic bulge tests, Nakajima tests for the forming limit curve (FLC), and cyclic tension-compression experiments. Results showed moderate planar anisotropy with R-values of 0.49–0.90, equi-biaxial yield stress around 105 MPa, and plane-strain FLC0 ≈ 0.25, typical for 6xxx-series alloys. The cyclic tests highlighted a strong Bauschinger effect and transient softening, which allowed precise calibration of the Yoshida-Uemori (Y-U) model. The resulting material parameters were validated using a U-bending case study, in which the predicted springback angle differed by only 2°, confirming the transferability of the calibrated model to forming conditions not used during parameter identification. The dataset generated in this work provides a robust foundation for finite element simulations of the AA6005C stamping processes and constitutes a practical reference for industrial implementation.

Alloys doi: 10.3390/alloys5010003

Authors: Shaopeng Wu Dongxin Wang Nairan Wang Xiaobo Ma Zhongxiong Xu Le Li Mingda Han Cheng Zhang

High-entropy alloys (HEAs) present a vast compositional design space, characterized by four core effects—high configurational entropy, sluggish diffusion, severe lattice distortion, and the cocktail effect—which collectively underpin their exceptional potential for both structural and hydrogen storage applications. This mini-review synthesizes recent advances in the compositional design of HEAs with emphasis on structural materials and hydrogen storage. Firstly, it provides an overview of the definition of HEAs and the roles of principal alloying elements, then synthesizes solid solution formation rules based on representative descriptors—atomic size mismatch, electronegativity difference, valence electron concentration, mixing enthalpy, and mixing entropy—together with their applicability limits and common failure scenarios. A brief introduction is provided to the preparation methods of arc melting and powder metallurgy, which have a strong interaction with the composition. The design–structure–property links are then consolidated for structural materials (mechanical properties) and for hydrogen storage materials (hydrogen storage performance). Furthermore, the rules for the combined design of control systems for HEAs and the associated challenges were further discussed, and the future development prospects of HEAs in structural materials and hydrogen storage were also envisioned.

Alloys doi: 10.3390/alloys5010002

Authors: Alexander Eliseev Olga Novitskaya

Friction extrusion technology was first developed and patented in 1991 at The Welding Institute, but it remained largely unexplored for many years. Over the past decade, this technology has gained popularity due to its ability to recycle chips and produce composite materials. Typically, in friction extrusion, the applied force and extrusion direction are opposite; this configuration is commonly referred to as reverse extrusion. Additionally, the tool feed rate is often used as a control parameter. However, this approach introduces technological challenges and results in a heterogeneous product structure. This paper proposes a novel friction extrusion method in which the applied force and extrusion direction are co-directional, and no tool is used. Moreover, a constant load is maintained throughout the extrusion process. Experimental results demonstrate that the proposed scheme is feasible and enables wire extrusion without macroscopic defects. Although the current efficiency is low and the maximum sample size achieved is 45 mm, the cross-sectional microhardness of the samples remains stable. The material strength reached approximately 90% of that of the initial 2024 aluminum alloy.

Alloys doi: 10.3390/alloys5010001

Authors: Mirsalim M. Asadov Solmaz N. Mustafaeva Saida O. Mammadova

Intermetallic alloys based on A15-type compounds, including cubic Ti3Sb, attract increasing interest due to their tunable electronic properties and potential for surface-related functional applications. Here, the interaction of nitrogen with Ti3Sb is systematically investigated using spin-polarized density functional theory within the GGA-PBE approximation. Nitrogen adsorption was analyzed on the Ti3Sb (111), (100), and (110) surfaces by considering top, bridge, and hollow sites at different surface coverages. Low nitrogen coverage was found to minimize lateral adsorbate interactions, allowing reliable evaluation of single-atom adsorption energies. Among the studied configurations, nitrogen adsorption at the hollow site of the Ti3Sb (111) surface is energetically most favorable. In addition, partial substitution of Ti or Sb atoms by nitrogen in Ti3Sb supercells was examined to assess its effect on bulk electronic properties. Nitrogen incorporation leads to pronounced modifications of the electronic band structure, density of states, and local magnetic moments, with a strong dependence on crystallographic direction. The calculated results reveal distinct electronic anisotropies originating from direction-dependent band dispersion and associated effective carrier masses. These findings clarify the role of nitrogen in tailoring both surface and bulk electronic characteristics of Ti3Sb and provide a theoretical basis for the targeted design of A15-type intermetallic materials for sensing, catalytic, and energy-related applications.

Alloys doi: 10.3390/alloys4040029

Authors: Nik Tankov Claire Utton Panos Tsakiropoulos

Some cast metallic alloys for ultra-high-temperature structural applications can have better mechanical properties compared with Ni-based superalloys. Research on the directional solidification (DS) of such alloys is limited. The production of DS components of these alloys with “tailor-made” microstructures in different parts of the component has not been considered. This paper attempts to address these issues. A bar of the RCCA/RM(Nb)IC with nominal composition 3.5Al–4Crc6Ge–1Hf–5Mo–36Nb–22Si–1.5Sn–20Ti–1W (at.%) was directionally grown using OFZ processing, where the growth rate R increased from 1.2 to 6 and then to 15 cm/h. The paper studies how the macrosegregation of the elements affected the microstructure in different parts of the bar. It was shown that the synergy of macrosegregation and growth rate produced microstructures from the edge to the centre of the OFZ bar and along the length of the OFZ bar that differed in type and chemical composition as R increased. Contamination with oxygen was confined to the “root” of the part of the bar that was grown with R = 1.2 cm/h. The concentrations of elements in the bar were related (a) to each of the parameters VEC, Δχ, and δ for different sections, (i) across the thickness and (ii) along the length of the bar, or to each other for different sections of the bar, and demonstrated the synergy and entanglement of processing, parameters, and elements. In the centre of the bar, the phases were the Nbss and Nb5Si3 for all R values. In the bar, the silicide formed with Nb/(Ti + Hf) less or greater than one. There was synergy of solutes in the solid solution and the silicide for all R values, and synergy and entanglement of the two phases. Owing to the synergy and entanglement of processing, parameters, elements, and phases, properties would “emerge” in each part of the bar. The creep and oxidation properties of the bar were calculated as guided by the alloy design methodology NICE. It was suggested that, in principle, a component based on a metallic UHTM with “functionally graded” composition, microstructure and properties could be directionally grown.

Alloys doi: 10.3390/alloys4040028

Authors: Veronika Utyaganova Alexey Goncharov Andrey Sliva Dmitry Shishkin Boris Zotov Leonid Fedorenko Viktor Semin

A thin-walled product made of AZ31 magnesium alloy was successfully fabricated using wire-feed electron-beam additive manufacturing. The microstructure of the initial wire, used as a precursor, comprises a α-Mg(Al, Zn) solid solution and a minor amount of the Al8Mn5 intermetallic phase. The microstructure of the as-printed AZ31 alloy exhibits a three-phase structure: α-Mg(Al, Zn), Al8Mn5, and β-Mg17Al12. It was proposed that the secondary β-phase was formed via a primary solidification process upon the cooling of the welded layers. The texture effect was evident in the <011¯2> direction, corresponding to the printing direction, while other crystallographic orientations demonstrated near-equal pole densities as the XRD lines. The yield strength for the as-printed alloy was found to be 86 MPa; the tensile strength reached 240 MPa; and the relative elongation was 21.5%. For the first time, the corrosion resistance of an EBAM-fabricated AZ31 alloy was studied. It was revealed that the corrosion current density in the referenced as-cast and as-printed alloys was below 2·10−4 A/cm2.

Alloys doi: 10.3390/alloys4040027

Authors: Mihail Kolev Vladimir Petkov Rumyana Lazarova Veselin Petkov Krasimir Kolev Shaban Uzun

Aluminum–copper alloys have garnered significant attention in modern engineering applications due to their exceptional strength-to-weight ratio, corrosion resistance, and thermal conductivity properties. This study investigates the tribological performance optimization of Al10Cu alloys through chromium coating deposition, focusing on coefficient of friction and mass wear analysis in dry sliding conditions. Cr-coated Al10Cu alloys were fabricated through powder metallurgy and electrodeposition techniques, with comprehensive tribological characterization performed using scanning electron microscopy combined with energy-dispersive X-ray spectroscopy, X-ray diffraction analysis, microhardness measurements, and dry sliding wear testing. The chromium coating exhibited exceptional surface hardness of 720.9 HV, representing a remarkable 15-fold improvement over the uncoated Al10Cu matrix hardness. Tribological evaluation demonstrated outstanding wear resistance with the Cr-coated Al10Cu system achieving only 0.10 mg mass loss compared to 0.55 mg for the uncoated alloy, representing an exceptional 81.8% reduction in material removal. Despite a nominal increase in the coefficient of friction from 0.618 to 0.733, the chromium coating effectively transformed the wear mechanism from severe material removal to a controlled mild wear regime. The results establish the Cr-coated Al10Cu system as a highly effective solution for applications requiring extended operational lifespans under dry sliding conditions.

Alloys doi: 10.3390/alloys4040026

Authors: Xudong Gao Jian Chen Yuelin Qin

Although the composition of hearth gas in a blast furnace is still composed of CO, H2, and N2, after injecting shale gas, which replaces some pulverized coal, the proportion of CO, H2, and N2 in the hearth gas will change with the introduction of H2. Further, the reduction process of vanadium-titanium magnetite sinter (VTMS) will be significantly impacted. Hence, the energy–mass balance and replacement ratio model was used to calculate the composition of hearth gas under different injection conditions using production data from a VTM blast furnace in the Panxi area of China. In order to investigate how shale gas injection affects the reduction process, the weight loss rates of VTMS under various reduction atmospheres were obtained through a series of thermogravimetric experiments. Additionally, X-ray diffraction (XRD) analysis was performed on select reduced samples to determine the alterations in sinter phases before and after the reaction. The impact of shale gas injection on the reduction process of VTMS was analyzed by phase transformation and kinetic analysis. The results of the research show that the reduction process of VTMS is improved with the increase in shale gas injection. Using the ln-ln analytical method, the linear relationship between ln(−ln(1 − α)) and lnt under different cases was found. The reaction mechanism of VTMS under shale gas injection circumstances is characterized by random nucleation, which is subsequently followed by growth. The integration formula associated with its dynamic function is G(α) = [−ln(1 − α)]3/4.

Alloys doi: 10.3390/alloys4040025

Authors: Arman Miniyazov Mazhyn Skakov Nuriya Mukhamedova Igor Sokolov Aisara Sabyrtayeva Ospan Oken Riza Zhakiya Zhanna Ospanova

In this work, the results of the structural and phase state of LaNi5-based alloys modified with Ti, Mn, and Co elements, obtained by mechanical alloying and subsequent spark plasma sintering, are presented. X-ray diffraction analysis was carried out to determine the phase composition, lattice parameters, microstrain, and average crystallite size, as well as to study the morphology and microstructure of the synthesized samples. It was established that the ball-to-powder ratio (BPR) and the milling speed affect the degree of intermetallic phase formation and the level of accumulated microstrains. The optimal mechanical alloying parameters make it possible to form the necessary precursor components for subsequent spark plasma sintering (SPS). It was determined that the SPS process effectively promotes the formation of intermetallic phases such as TiNi, LaNi4Mn, LaNi3Mn2, and LaNi4Co, ensuring high crystallinity and a reduction in defects accumulated during mechanical alloying. The morphology and microstructure of the samples with titanium, manganese, and cobalt additions showed that at the mechanical alloying stage, all systems are characterized by a dispersed and agglomerated structure, a wide particle size distribution, and a developed surface. After SPS, all series exhibited material consolidation and the formation of a dense matrix with distinct grain boundaries.

Alloys doi: 10.3390/alloys4040024

Authors: Andrei Filatov Eugene Goli-Oglu Vitaliy Naumenko Alexander Kazarin

The quality of heavy plates produced from low-carbon steel is directly linked to the structural characteristics inherited from the initial continuously cast thick slabs. This study explores how different casting technologies affect the morphology and distribution of allotriomorphic ferrite along prior austenite grain boundaries (PAGBs) within these slabs. Using quantitative microstructural analysis based on advanced computer vision techniques (OpenCV), the research identifies significant variations in ferrite boundary thickness and volume fraction associated with different casting methods. These microstructural differences strongly correlate with variations in Charpy V-notch impact energy (KVZ20) and susceptibility to microcrack formation during subsequent rolling processes. The results obtained allow us to evaluate the influence of the cast structure on the formation of the initial structural characteristics of the material, especially on the formation of microcracks of the slab microstructure and their propagation during further processing.

Alloys doi: 10.3390/alloys4040023

Authors: Zhi Zhu Yikun Fang Wei Wu Bo Zhao

Understanding the way samarium–cobalt alloys solidify at varying cooling rates and the regularities in alloying element distribution is crucial for optimizing subsequent homogenization and annealing processes, leading to an enhancement in the overall quality of the product. The study investigates the effects of rapid water-cooled copper mold (600 °C/min), medium-speed copper mold (100 °C/min), and slow furnace cooling (10 °C/min) on the microstructural evolution, element distribution, and phase transformation of samarium–cobalt (Sm-Co) alloys. The results of the research show that the phase transition temperatures obtained via differential scanning calorimetry (DSC) closely matched those observed in situ by high-temperature laser scanning confocal microscopy (HT-LSCM). Higher cooling rates resulted in notable dendritic refinement and reduced precipitate size. Elemental analysis revealed that Co and Fe exhibited negative segregation, whereas Sm, Cu, and Zr showed positive segregation, with segregation intensity increasing alongside the cooling rate. The principal phases identified included Cu-rich and Zr-rich constituents, the matrix phase, and a gray phase morphologically distinct from the matrix. These correspond to the (Sm, Co, Fe, Cu, Zr)5 phase, (Sm, Zr)(Co, Fe, Cu)3 phase, Sm2(Co, Fe, Cu, Zr)17 phase, and Sm(Co, Fe, Cu, Zr)7 phase. The phase constitution remained consistent across different cooling rates.

Alloys doi: 10.3390/alloys4040022

Authors: Mihail Kolev Juliana Javorova Tatiana Simeonova Yasen Hadjitodorov Boyko Krastev

Understanding the intricate relationship between composition, processing conditions, and material properties is essential for optimizing Cu-based alloys. Machine learning offers a powerful tool for decoding these complex interactions, enabling more efficient alloy design. This work introduces a comprehensive machine learning framework aimed at accurately predicting key properties such as hardness and electrical conductivity of low-alloyed Cu-based alloys. By integrating various input parameters, including chemical composition and thermo-mechanical processing parameters, the study develops and validates multiple machine learning models, including Multi-Layer Perceptron with Production-Aware Deep Architecture (MLP-PADA), Deep Feedforward Network with Multi-Regularization Framework (DFF-MRF), Feedforward Network with Self-Adaptive Optimization (FFN-SAO), and Feedforward Network with Materials Mapping (FFN-TMM). On a held-out test set, DFF-MRF achieved the best generalization (R2_test = 0.9066; RMSE_test = 5.3644), followed by MLP-PADA (R2_test = 0.8953; RMSE_test = 5.7080) and FFN-TMM (R2_test = 0.8914; RMSE_test = 5.8126), with FFN-SAO slightly lower (R2_test = 0.8709). Additionally, a computational performance analysis was conducted to evaluate inference time, memory usage, energy consumption, and batch scalability across all models. Feature importance analysis was conducted, revealing that aging temperature, Cr, and aging duration were the most influential factors for hardness. In contrast, aging duration, aging temperature, solution treatment temperature, and Cu played key roles in electrical conductivity. The results demonstrate the effectiveness of these advanced machine learning models in predicting critical material properties, offering insightful advancements for materials science research. This study introduces the first controlled, statistically validated, multi-model benchmark that integrates composition and thermo-mechanical processing with deployment-grade profiling for property prediction of low-alloyed Cu alloys.

Alloys doi: 10.3390/alloys4040021

Authors: Qian Qiao Hongchang Qian Zhong Li Dawei Guo Chi Tat Kwok Shufei Jiang Dawei Zhang Lam Mou Tam

An AA6061-7075 composite with a heterogeneous structure was fabricated via the additive friction stir deposition (AFSD) method, and in situ processing data were monitored during the manufacturing process. The results show that the cross-section of the composite subjected to AFSD exhibits a lower degree of plastic deformation behavior compared to the surface and side of the composite, owing to serious heat accumulation during the layer-by-layer stacking process. The denser, heterogeneous structure, consisting of finer (softer) and coarser (harder) grains, which correspond to AA6061 and AA7075, was formed according to transmission electron microscopy (TEM) analysis. Furthermore, the obtained composite subjected to AFSD in this work presents outstanding mechanical properties compared to other as-fabricated AA6061/AA7075 depositions acquired by other additive manufacturing methods along the horizontal building direction, with the ultimate tensile strength (266 MPa) being 89% of that of AA6061-T6 and the elongation 1.1 times that of AA7075-T6. The findings provide useful guidelines for the in situ preparation of Al-based composites and offer ideas for manufacturing high-strength heterostructures for large-scale practical engineering applications.

Alloys doi: 10.3390/alloys4040020

Authors: Gloria Zlatić Jelić Ivana Martinović Zora Pilić

The combination of electrochemical, surface, and spectroscopic techniques revealed that Pseudomonas aeruginosa biofilm accelerated corrosion of 304 stainless steel (SS), leading to localized pitting with depths up to 3.75 μm. Such damage did not occur on 304 SS treated with P. aeruginosa in the presence of Artemisia annua L. extract, or in sterile seawater. Introducing A. annua into biotic seawater hindered biofilm development and prevented the formation of porous Fe(III) corrosion products. Instead, a compact Fe3O4 layer formed, indicating a shift in corrosion product morphology and stability. ATR-FTIR analysis confirmed phenolic groups from the extract were adsorbed onto the steel interface, supporting the dual inhibitory role of A. annua through both surface modification and antimicrobial action. A. annua extract demonstrated a 74.4 ± 4.4% reduction in MIC-induced corrosion of 304 SS in marine conditions.

Alloys doi: 10.3390/alloys4030019

Authors: Mohamed Almatroushi Salman Pervaiz Wael A. Samad

Under specific temperature and strain rate conditions, certain materials, such as low-carbon steels and select magnesium and aluminum alloys, experience a localized deformation phenomenon known as the Lüders effect. This behavior manifests as a well-defined yield point, after which the stress–strain response transitions into a plateau phase. Experimentally observed through full-field tests, the Lüders effect appears in the form of a band(s). This manuscript presents, for the first time, a systematic study of interrupted loading on the Lüders phenomenon in AISI 1524 hot-rolled steel, using uniaxial tensile testing combined with digital image correlation (DIC). While similar approaches have been applied to other alloys, no prior work has reported on AISI 1524 steel under unloading–reloading cycles during the Lüders plateau. Interruptions in loading involved unloading at 25%, 50%, and 75% of the total plateau region independently until stress approached zero, followed by reloading at the same rate until failure. Each unloading case was subjected to two tests, alongside two additional control tests where loading proceeded without interruption. Based on the findings of this study, it can be inferred that the Lüders phenomenon in AISI 1524 steel exhibits a decrease in strain intensity upon unloading, along with an extension of the Lüders plateau when interrupted loading occurs up to halfway through the plateau region. However, implementing an interrupted loading regime at three-quarters of the plateau had minimal to no discernible effect on the phenomenon. The majority of samples displayed two Lüders bands, a few exhibited either a single band or three bands, suggesting a complex relationship with material heterogeneity and specific impurities present in each sample. The novelty of this work lies in showing how controlled unloading–reloading cycles alter both the propagation and characteristics of Lüders bands in AISI 1524 steel.

Alloys doi: 10.3390/alloys4030018

Authors: Surendra Kumar Patel Lei Shi

Aluminium metal matrix composites (AMMCs) incorporate aluminium alloys reinforced with fibres (continuous/discontinuous), whiskers, or particulate. These materials were engineered as advanced solutions for demanding sectors including construction, aerospace, automotive, and marine. Micro- and nano-scale reinforcing particles typically enable attainment of exceptional combined properties, including reduced density with ultra-high strength, enhanced fatigue strength, superior creep resistance, high specific strength, and specific stiffness. Microstructural, mechanical, and tribological characterizations were performed, evaluating input parameters like reinforcement weight percentage, applied normal load, sliding speed, and sliding distance. Fabricated nanocomposites underwent tribometer testing to quantify abrasive and erosive wear behaviour. Multiple investigations employed the Taguchi technique with regression modelling. Analysis of variance (ANOVA) assessed the influence of varied test constraints. Applied load constituted the most significant factor affecting the physical/statistical attributes of nanocomposites. Sliding velocity critically governed the coefficient of friction (COF), becoming highly significant for minimizing COF and wear loss. In this review, the reinforcement homogeneity, fractural behaviour, and worn surface morphology of AMMCswere examined.

Alloys doi: 10.3390/alloys4030017

Authors: Aikaterini Baxevani Eleni Lamprou Azarias Mavropoulos Fani Stergioudi Nikolaos Michailidis Ioannis Tsoulfaidis

Aluminum is widely used in many industries like automotive, aerospace and construction because of its low weight, good mechanical strength and resistance to corrosion. This resistance comes mainly from a passive oxide layer that forms on its surface. However, when aluminum is exposed to harsh environments, especially those containing chloride ions in marine environments, this layer can break down and lead to localized corrosion, such as pitting. This study examined aluminum profiles at different processing stages, including homogenization and aging, anodizing and pre-anodizing followed by painting. Corrosion behavior of samples was studied using two electrochemical methods. Potentiodynamic polarization was used to measure corrosion rate and current density, while Electrochemical Impedance Spectroscopy (EIS) helped to understand the behavior of protective layers and corrosion progression. Tests were carried out in a 3.5% NaCl solution at room temperature. EIS results were analyzed using equivalent circuit models to better understand electrochemical processes. Overall, this study shows how surface treatment affects corrosion resistance and highlights advantages of EIS in studying corrosion behavior in a more reliable and repeatable way.

Alloys doi: 10.3390/alloys4030016

Authors: Alessandra Ceci Girolamo Costanza Fabio Giudice Andrea Sili Maria Elisa Tata

The global pursuit of a sustainable and decarbonized energy landscape requires the development of novel materials capable of supporting lightweight construction, advanced energy conversion, storage, and thermal management technologies. Among these, metal foams have emerged as a versatile class of porous materials, offering a unique combination of low density, high surface area, three-dimensional (3D) interconnected porosity, and favorable thermal and electrical conductivities. These attributes make them highly suitable for a broad range of applications critical to the ongoing energy transition, assuming an increasingly central role in enabling clean, efficient, and resilient energy infrastructures. From this key perspective, the present review highlights the relevance of the adoption of metal foams in several fields crucial for the energy transition. By presenting methodologies and outcomes of research results, mainly from the last five years, the paper underscores the potential of low-weight, high-surface, and high-performance porous materials in contemporary and future industry, supporting sustainable development and, more generally, energy transition and circular economy. The approach also aims to minimize negative impacts and promote sustainability, for example, by recycling and transforming waste materials.

Alloys doi: 10.3390/alloys4030015

Authors: Victor I. Stanciu Alexandre Mégret Anne Mouftiez Véronique Vitry Fabienne Delaunois

Cemented carbides are among the primary materials for tools and wear parts. Today, energy prices and carbon emissions have become key concerns worldwide. Cemented carbides consist of tungsten carbide combined with a binder, typically cobalt, nickel, or more recently, various high-entropy alloys. Producing tungsten carbide involves reducing tungsten oxide, followed by carburization of tungsten at 1400 °C under a hydrogen atmosphere. The tungsten carbide produced is then mixed with the binder, milled to achieve the desired particle size, and granulated to ensure proper flow for pressing and shaping. This study aims to bypass the tungsten carburizing step by mixing tungsten, carbon, and cobalt; shaping the mixture; and then applying reactive sintering, which will convert tungsten into carbide and consolidate the parts. The mixtures were prepared by planetary ball milling for 10 h under different conditions. Tests demonstrated that tungsten carburization successfully occurs during sintering at 1450 °C for 1 h. The samples exhibit a typical cemented carbide microstructure, characterized by prismatic grains with an average size of 0.32 μm. Densification reached 92%, hardness is approximately 1800 HV30, and toughness is 10.9 ± 1.15 MPa·m1/2.

Alloys doi: 10.3390/alloys4030014

Authors: Dorjsuren Bolormaa Maashaa Dovchinvanchig

This research investigates the effects of the addition of the rare-earth element La on the microstructure, phase transformation, and mechanical properties of Ni50Ti30Hf20−xLax (x = 0, 0.5, 1, 2) alloys. The results show that a primary matrix composed of Ni-Ti-Hf and featuring La-rich second phases formed. The temperature at which the martensitic phase transformation starts decreases with an increase in La content. As the amount of La increases, hardness decreases slightly, while the elastic modulus increases.

Alloys doi: 10.3390/alloys4030013

Authors: Thanh-Trung Nguyen

This study investigates the effect of ultrasonic vibration applied in the cutting speed direction on surface quality during face turning of C45 steel. The experiments were performed using an ultrasonic generator operating at a frequency of 20 kHz with an amplitude of approximately 10 µm. The cutting parameters used in the experiments included spindle speeds of 700, 1100, and 1300 rpm, feed rates of 0.1 and 0.15 mm/rev, while the depth of cut was fixed at 0.2 mm. Surface quality was evaluated based on the roughness parameters Ra and Rz, as well as surface topography was observed using a Keyence VHX-7000 digital microscope. The results show that ultrasonic-assisted face turning (UAFT) significantly improves surface finish, particularly in the central region of the workpiece where the cutting speed is lower and built-up edge (BUE) formation is more likely. The lowest Ra value recorded was 0.91 µm, representing a 71% reduction compared to conventional turning (CT). Furthermore, at the highest spindle speed (1300 rpm), the standard deviations of both Ra and Rz were minimal, indicating improved surface consistency due to the suppression of BUE by ultrasonic vibration. Topographical observations further confirmed that UAFT generated regular and periodic surface patterns, in contrast to the irregular textures observed in CT.

Alloys doi: 10.3390/alloys4030012

Authors: Reylina Garcia Tayactac Mark Christian E. Manuel Jaime P. Honra Tiago Bohn Kaspary Raimundo Cabral de Medeiros

Alloy 625 is a widely utilized nickel-based superalloy known for its excellent mechanical strength and corrosion resistance in aggressive environments. However, its high niobium (Nb) content can lead to the formation of detrimental phases, such as Laves and MC carbides, during welding processes, compromising the mechanical integrity and long-term performance of the weld overlay. This review systematically examines recent research findings on the implications of reducing Nb content in Alloy 625 weld overlays, particularly with respect to microstructure evolution, mechanical behavior, and corrosion performance. Key advancements, including the understanding of segregation behavior, solidification paths, and secondary phase formation, are presented based on recent studies. This paper aims to provide a discussion on the trade-offs and future directions for optimizing Alloy 625 weld overlay claddings through Nb content modification.

Alloys doi: 10.3390/alloys4030011

Authors: Zhang Wei Honglin Shu Gaixiao Qiao Qunfeng Zeng Guoping Wang Qian Jia

Babbitt alloys are among the most commonly used materials for sliding bearings. However, with the high speeds and heavy loads of modern machinery, as well as the demands of extreme working conditions, the temperature resistance, strength, and hardness of traditional Babbitt alloys are often insufficient to meet these requirements. To address this issue, it is essential to improve the properties of Babbitt alloys, particularly their performance at high temperatures. The present study explored a technical approach for incorporating copper powder to improve the high-temperature performance of Babbitt alloys. Copper powder was added to the traditional Babbitt alloy in mass percentages of 1, 2, 3, and 4%. After fabrication, the samples were examined using metallographic structure analysis, high-temperature compression testing, and friction and wear testing. The experiments investigated the effects of copper powder addition on the properties of the Babbitt alloy and determined the optimal amount of copper powder required to enhance its performance.

Alloys doi: 10.3390/alloys4020010

Authors: Bakhtiyar Suleyev Aristotel Issagulov Ardak Dostayeva Dastan Aubakirov Togzhan Sultanbek

This study examines the effect of silicon and manganese addition on the phase composition and electrical properties of Al-Fe alloys using both experimental methods and thermodynamic modeling with the ThermoCalc software package. This research focuses on the Al–Fe–Si–Mn system, which shows potential for developing conductive aluminum alloys with enhanced performance characteristics. It was found that when silicon and manganese are added in amounts up to 0.6%, the formation of intermetallic phases such as Al8Fe2Si and Al15Mn3Si2 occurs. These phases significantly influence the electrical conductivity and mechanical stability of the alloy. Thermodynamic modeling proved effective in predicting phase formation, guiding the selection of alloy compositions, and optimizing heat treatment parameters. The optimal composition for a conductive aluminum alloy includes up to 0.8% Fe, 0.5% Si, and 0.6% Mn. Heat treatment in the range of 500–550 °C resulted in a favorable combination of strength, electrical conductivity, and thermal resistance. The findings support the use of Al–Fe–Si–Mn alloys in electrical and structural applications and demonstrate the value of combining computational and experimental approaches in alloy design.

Alloys doi: 10.3390/alloys4020009

Authors: Abdulkerim Karaman Alexander Kremer Michael Marré

The increasing restriction of lead in industrial alloys, particularly in copper–zinc-based materials such as CuZn40Pb2, necessitates the development of environmentally safer alternatives. ZnAl15Cu1Mg (ZEP1510), a zinc-based wrought alloy composed of 15% aluminum, 1% copper, 0.03% magnesium, with the remainder being zinc, has emerged as a promising candidate for lead-free applications due to its favorable forming characteristics and corrosion resistance. This study investigates the performance of ZEP1510 compared to conventional leaded copper alloys and galvanized steel. Corrosion behavior was evaluated using neutral salt spray testing, cyclic climate chamber exposure, and electrochemical potential analysis in chloride- and sulfate-containing environments. ZEP1510 exhibited corrosion resistance comparable to brass and significantly better performance than galvanized steel in neutral and humid atmospheres. Combined with its low processing temperature and high recyclability, ZEP1510 presents itself as a viable and sustainable alternative to brass with lead for applications in sanitary, automotive, and electrical engineering industries.

Alloys doi: 10.3390/alloys4020008

Authors: Junli Guo Qiang Hu Kai Hu

Semi-continuous casting is an important method for the large-scale production of high-strength conductive copper-iron (Cu-Fe) alloys in the future. However, serious peeling defects were found on the surface of cold-rolled strips during industrial trials. Due to the multi-step complexity of the manufacturing process (from casting to final product), identifying the root cause of defect formation remains challenging. X-ray computed tomography (X-CT) was used to quantitatively characterize the pores and defects in the horizontal continuous casting Cu-Ni-Sn slab, the semi-continuous casting Cu-Fe alloy slab, and the hot-rolled slab of Cu-Fe, and the relationship between the defect characteristics and processes was analyzed. The results showed that the internal defect sphericity distribution of the Cu-Fe alloy slab after hot rolling was similar to that of the reference Cu-Ni-Sn slab. The main difference lies in the low sphericity range (<0.4). The volume of pore defects inside the Cu-Fe alloy after hot rolling was significantly larger than in the reference sample, with a 52-fold volume difference. This phenomenon may be the source of surface-peeling defects in the subsequent cold-rolling process. The occurrence of internal defects in the Cu-Fe alloy is related to both the composition characteristics and casting processes of the Cu-Fe alloy; on the other hand, it is also related to the hot-rolling process.

Alloys doi: 10.3390/alloys4020007

Authors: Mingyi Zhang Yang Li Chongyuan Huang Puyou Ying Yong Huan Chong Zhao Chi Xiao Fei Liu

Stacking fault energy (SFE) can significantly affect the plastic deformation mechanism of metal materials and then affect their mechanical properties. Changing the stacking fault energy by microalloying rare earth elements is an effective means to control the plastic deformation mechanism and optimize the mechanical properties of the metal materials. Based on first principles, the HRTEM technique and GPA method, the effects of Nd content on the SFE and microstructure of Cu alloys were studied. The results show that the Nd element can significantly reduce the SFE of pure copper. But the change in the Nd element content has little influence on the SFE of the alloy. In addition, with the increase in Nd content, the grain size and twin size are refined. The GPA results show that strong tensile strain is formed inside the twin, and alternating tensile strain and compressive strain structures are formed on the (-11-1) plane at the tip of the twin.

Alloys doi: 10.3390/alloys4020006

Authors: Eugene Goli-Oglu Marco Palombo Andrei Filatov

Using the results from testing industrial batches of 23 mm steel heavy plates after thermomechanical rolling and subsequent post-weld heat treatment, the patterns of fatigue crack formation in the fracture specimens during CTOD (Crack Tip Opening Displacement) testing for fracture toughness are investigated. Visual, microstructural, and fractographic studies of the nature of fracture formation and the surface of the secondary separations have been conducted. The probable causes of the manifestation of the potential “pop-in” effect on the load–displacement diagrams of the notch opening displacement are described, as well as its potentially negative impact on the interpretation of test results.

Alloys doi: 10.3390/alloys4020005

Authors: Abdul Munam Khan Uzma Zahoor

First-principles calculations were carried out to investigate the physical properties of the full-Heusler compound In2MnW. The WIEN2K code was utilized with various approximations, such as GGA and GGA+U, to analyze its structural, electronic, and magnetic properties. The unit cell was optimized to determine the ground-state energy. The calculated formation enthalpy (ΔH) of In2MnW is −0.189 eV, indicating its thermodynamic stability due to the negative value. Band structure analysis using both potentials confirms the compound’s metallic nature, which is further supported by total density of states calculations. The total magnetic moment is found to be 4.3 µB, which slightly increases to 4.4 µB when the U parameter is included. These findings suggest that In2MnW demonstrates metallic ferromagnetic behavior, highlighting its potential as a promising ferromagnetic material for mass storage applications.

Alloys doi: 10.3390/alloys4010004

Authors: Shanshan Cui Shiqing Wang Yiqiang Zhang Guodong Wen Wei Qiang

In this paper, TC4 titanium alloy pipes were achieved by continuous drive friction welding, metallographic microscope and microhardness tester were used to evaluate the microstructure and the hardness of the joints, and the effect of friction pressure on the microstructure was studied. Under the selected welding parameters, all the joints have good morphology. The martensite is formed at the weld zone and the flash, which leads to a higher hardness on the weld zone. With the increase of friction pressure, the width of the weld zone, the grain size and LAGB (low angle grain boundary) at the weld zone decreases. In addition, dynamic recrystallization increases first, but when the friction pressure reaches 65 MPa, the deformation dominates.

Alloys doi: 10.3390/alloys4010003

Authors: Prince Sharma

Half-Heusler alloys are promising materials for thermoelectric applications, yet the impact of the compositional disorder on their lattice dynamics remains incompletely understood. This study investigates the effect of systematic Zr substitution on the lattice dynamics and thermal properties of TixZr1-xNiSn half-Heusler alloys using first-principles calculations. Through careful analysis of phonon dispersions, density of states, and thermodynamic properties, it is revealed that Zr substitution (25%, 50%, and 75%) introduces minimal structural distortion while enhancing system stability. It is shown that increasing Zr content systematically modifies the phonons, particularly affecting the high-frequency optical modes above 5 THz. Notably, with Zr content, these findings provide valuable insights for tailoring the thermal properties of half-Heusler alloys for high-temperature applications in thermoelectric devices and components.

Alloys doi: 10.3390/alloys4010002

Authors: Irakli Nakhutsrishvili Revaz Tevzadze

This paper discusses the influence of the secondary processes of reaction product evaporation and the reduction of the effective diffusion area into the scale on the kinetics (change in sample mass–time) of the high-temperature oxidation processes, in air, of alumina- and chromia-forming alloys.

Alloys doi: 10.3390/alloys4010001

Authors: Huixing (Hannah) Zhang Caitlin E. R. Green Maria J. Lodeiro Peter Woolliams Ken P. Mingard Antony T. Fry

For additive manufactured parts, it is important to measure homogeneity and demonstrate representative parts can be printed faster while maintaining key mechanical properties. In this work, a multiscale characterization of microstructural and mechanical properties was carried out to gain a thorough understanding of a range of powder bed fusion-laser beam (PBF-LB)-manufactured Scalmalloy for future optimization of the processing parameters. The relationship between microstructure, including porosity, grain structure, and precipitates, and mechanical properties, is investigated. The stress-relieved samples were characterized mainly using scanning electron microscopy (SEM) suite, uniaxial tensile tests and nanoindentation. The results show the multiple strengthening mechanisms in Scalmalloy, including solid solution strengthening, grain size, precipitates and dislocations strengthening, demonstrated through a combination of the nanoindentation measurements with microstructural analysis at the local scale. The current work suggests potential mechanisms for further improvement of the strength and ductility in PBF-LB-Scalmalloy.

Alloys doi: 10.3390/alloys3040018

Authors: Tahmina Keya Ralf D. Fischer Mohanish Andurkar Scott M. Thompson Valentina O’Donnell John Gahl Barton C. Prorok

Laser powder bed fusion (L-PBF) is a metal additive manufacturing (AM) technique that produces a unique microstructure significantly different from wrought microstructure. Inconel 625 (IN625) is an alloy widely used to manufacture complex parts, but it comes with its own unique challenges. The alloy is prone to precipitation under elevated temperatures, which makes designing suitable heat treatment to tailor the desired microstructure and mechanical properties critical. Traditional heat treatment for wrought IN625 cannot be applied to L-PBF IN625; therefore, it is vital to understand the evolution of precipitates on the way to complete recrystallization. This study focuses on these precipitates in IN625 produced by the L-PBF technique. Heat treatments at 700 °C, 900 °C, and 1050 °C were performed separately to encourage the precipitation of strengthening γ″, the detrimental δ phase, and the dissolution of precipitates, respectively. γ″ precipitates were found in the as-printed condition and at 700 °C. δ precipitates were detected at 700 and 900 °C. Carbides and Al-rich oxides were observed in all conditions of L-PBF IN625. Texture analysis showed grain growth along the build direction with strong (100) texture at temperatures up to 900 °C. Weak and random texture with equiaxed grains was observed at 1050 °C, which is similar to wrought IN625.

Alloys doi: 10.3390/alloys3040017

Authors: Albin Gottwalt-Baruth Paul Kubaschinski Manuela Waltz Ulrich Tetzlaff

The fatigue behavior of a fully processed, non-oriented electrical steel sheet is investigated in dependence on shear-cutting parameters and a subsequent heat treatment. For this, stress-controlled fatigue tests are performed before and after annealing at 700 °C for a total of six different shear-cutting settings. For all parameters, the fatigue strength of shear-cut sheets is improved by the heat treatment. This is due to reduction in a large part of the strain hardening region as well as the reduction in tensile residual stresses. Both were introduced during shear cutting and act detrimental to the fatigue strength. However, the intensity of this improvement depends on the shear-cutting parameters. This is related to the corresponding edge surfaces characteristically being formed during shear cutting. Specimens cut with a worn cutting tool show a more pronounced increase in fatigue life. In contrast, specimens produced with a sharp-edged cutting tool and high cutting clearance hardly benefit from the heat treatment. This appears to be caused by differences in surface topography, in particular coarse topographical damage in the form of grain breakouts. If these occur during shear cutting, the crack formation is not significantly delayed by additional annealing.

Alloys doi: 10.3390/alloys3040016

Authors: Bo Xu Yangtao Xu Jianglong Wei

Co-Cr-Mo alloy as a human body implant material has a long history, because of its excellent corrosion resistance and biocompatibility, and is widely used in human hip joint materials. Co-Cr-Mo alloy in the human body is often in a passivation state; the formation of dense oxide film on the alloy surface prevents further corrosion of the alloy. The main component of the passivation film is the oxide of Cr, so a layer of oxide film formed by Cr on the surface of Co-Cr-Mo alloy is the reason for its good corrosion resistance. In biocompatibility, cytotoxicity is the first choice and necessary option for biological evaluation, and cytotoxicity can quickly detect the effect of materials on cells in a relatively short time. Therefore, this research conducted a comparative evaluation on the corrosion resistance and biocompatibility of forged Co-Cr-Mo alloys produced in domestic and foreign alloys in line with medical standards. Three simulated human body fluids and Princeton electrochemical station were selected for corrosion resistance experiments, and it was found that the corrosion resistance of four alloys in sodium citrate solution inside and outside China would be reduced. All the alloys exhibit secondary passivation behavior in Hanks solution, which improves the corrosion resistance of the alloys. According to the self-corrosion potential Ecorr analysis, the corrosion resistance of domestic B alloy is the best, while that of foreign R31537 alloy is poor. In the biocompatibility experiment, the biocompatibility of Co-Cr-Mo alloy was evaluated through the measurement of contact Angle and cytotoxicity reaction. The experimental results show that Co-Cr-Mo alloy is a hydrophilic material, and the contact Angle of foreign R31537 alloy is smaller, indicating that the surface of R31537 alloy is more suitable for cell adhesion and spreading. According to the qualitative and quantitative analysis of the cytotoxicity experiment, the toxic reaction grade of domestic A, B and R31537 alloy is grade 1, the toxic reaction grade of C alloy is grade 2, and C alloy has a slight toxic reaction.

Alloys doi: 10.3390/alloys3040015

Authors: Surinder Pal Xavier Velay Waqas Saleem

This study investigates the corrosion behavior of Grade 23 Ti6Al4V alloys produced through laser powder bed fusion (L-PBF) when exposed to simulated body fluid at room temperature, focusing on the role of unmelted particles. This research aims to understand how these microstructural features, resulting from the additive manufacturing process, influence the corrosion resistance of the alloys. It was observed that unmelted particles serve as critical sites for initiating localized corrosion, including pitting, which significantly compromises the material’s overall durability. Electrochemical testing and detailed surface analysis revealed that these particles, alongside other defects such as voids, exacerbate the susceptibility to corrosion in biomedical environments where high material reliability is paramount. Weight loss measurements conducted over exposure periods of 48 h, 96 h, and 144 h demonstrated a progressive increase in corrosion, correlating with the presence of unmelted particles. These findings underscore the importance of optimizing L-PBF processing parameters to minimize the formation of unmelted particles, thereby enhancing corrosion resistance and extending the operational lifespan of Ti6Al4V implants in biomedical applications.

Alloys doi: 10.3390/alloys3030014

Authors: Nikita Cherezov Andrey Fadeev Andrey Samokhin Mikhail Alymov

Additive manufacturing is a promising and actively developing method for the synthesis of metal products. The development of techniques for the production of spherical powder particles with specified properties from metals and alloys represents a significant challenge in the field of additive manufacturing. A new method for the production of titanium powders with spherical particles has been proposed, including the method of hydrogenation and dehydrogenation with subsequent spheroidization in thermal plasma. Titanium sponge, used as a feedstock, was saturated with hydrogen using the energy-efficient self-propagating high-temperature synthesis (SHS) method. The resulting hydride was then mechanically ground and then dehydrogenated by thermal decomposition in a vacuum furnace. The resulting precursor was subjected to plasma treatment, which resulted in a product (titanium powder) with a high degree of spheroidization. The physical, chemical, and technological parameters of the titanium powders were investigated. It was found that the final product, spherical titanium powder, has the necessary properties for use in additive manufacturing technologies.

Alloys doi: 10.3390/alloys3030013

Authors: Anatoly Mukhachev Dmytro Yelatontsev Olena Kharytonova Nickolay Grechanyuk

The paper presents the results of the study of the processes of self-propagating high-temperature synthesis of Zr-1%B alloy and its refining by electron beam melting. Experiments on the influence of boron’s amorphous and crystalline modifications on the safety parameters of the synthesis process of Zr-1%B alloy necessitated the conversion of amorphous boron into crystalline form by electron beam melting, with an increase in its purity from 94% to 99.9%. High efficiency of vacuum induction and electron beam equipment was demonstrated, which provided a high purity of the Zr-1%B alloy of at least 99.9%. The alloy ingots had a uniform distribution of the alloying element (boron) all over the volume. The obtained alloy is suitable for the production of materials with thermal neutron capture cross-sections of up to 40 barns for neutron protection.

Alloys doi: 10.3390/alloys3030012

Authors: Nik Tankov Claire Utton Panos Tsakiropoulos

Abstract: The refractory complex concentrated alloy (RCCA) 5Al–5Cr–5Ge–1Hf–6Mo–33Nb–19Si–20Ti–5Sn–1W (at.%) was studied in the as-cast and heat-treated conditions. The partitioning of solutes in the as-cast and heat-treated microstructures and relationships between solutes, between solutes and the parameters VEC and Δχ, and between these parameters, most of which are reported for the first time for metallic UHTMs, were shown to be important for the properties of the stable phases A15–Nb3X and the D8m βNb5Si3. The nano-hardness and Young’s modulus of the A15–Nb3X and the D8m βNb5Si3 of the heat-treated alloy were measured using nanoindentation and changes in these properties per solute addition were discussed. The aforementioned relationships, the VEC versus Δχ maps and the VEC, Δχ, time, or VEC, Δχ, Young’s modulus or VEC, Δχ, nano-hardness diagrams of the phases in the as-cast and heat-treated alloy, and the properties of the two phases demonstrated the importance of synergy and entanglement of solutes, parameters and phases in the microstructure and properties of the RCCA. The significance of the new data and the synergy and entanglement of solutes and phases for the design of metallic ultra-high temperature materials were discussed.

Alloys doi: 10.3390/alloys3030011

Authors: Serhii Teslia Mykyta Kovalenko Mariia Teslia Mykhailo Vterkovskiy Ievgen Solodkyi Petro Loboda Tetiana Soloviova

Light alloys based on magnesium are widely used in most areas of science and technology. However, magnesium powder alloys are quite difficult to sinter due to the stable film of oxides that counteracts diffusion. Therefore, finding a method to activate magnesium sintering is urgent. This study examines the effect of adding 5 wt. % and 10 wt. % zinc to the sintering pattern of magnesium powders at 430 °C; a dwell of 30 min was used to homogenize at the densification’s temperature. Scanning electron microscopy (SEM) was used to characterize the alloy’s microstructure, while the phase composition was characterized using X-ray diffraction (XRD) and energy dispersion spectroscopy (EDS). The sintering densities of Mg–5Zn and Mg–10Zn were found to be 88% and 92%, respectively. The results show that after sintering, a heterophase structure of the alloy is formed based on a solid solution and phases MgZn and Mg50Zn21. To establish the sintering mechanism, the interaction at the MgO and Zn melt phase interface was analyzed using the sessile drop method. The minimum contact angle—65°—was discovered at 500 °C with a 20 min holding time. It was demonstrated that the sintering process in the Mg–Zn system proceeds through the following stages: (1) penetration of zinc into oxide-free surfaces; (2) crystallization of a solid solution, intermetallics; and (3) the removal of magnesium oxide from the particle surface, with oxide particles deposited on the surface of the sample.

Alloys doi: 10.3390/alloys3030010

Authors: Weijun Huang Yajing Liu Tao Jiang

An innovative technology for the direct reduction of copper slag was studied while smelting Cu-Fe alloy by carbon to recover the main valuable elements from the copper smelting slag. The melting temperature of samples first decreased, followed by an increase in Fe3O4 content in slag. The melting temperature reached the minimum temperature of 1157 °C once the Fe3O4 content was about 8 wt%. The recovery rate of copper and iron first increased gradually, followed by a rapid increase in the modifier (CaO). Subsequently, the rise in the recovery rate slowed down. The reduction rate of copper and iron only increased by 1.61% and 1.05% from 5 wt% CaO to 10 wt% CaO, but significantly increased by 8.89% and 14.21% from 10 wt% CaO to 25 wt% CaO, and remained almost unchanged beyond 25 wt% CaO. This could be attributed to the reaction between modifier (CaO) and silicate in acidic copper slag to generate low melting point composite oxide while replacing free iron oxides, improving the melting properties and reduction reaction. Meanwhile, the recovery rates of copper and iron increased with the increase of reaction time, reaction temperature, and reduction agent in a certain range. To obtain good element yield, the optimum conditions for reducing copper and iron from the molten copper slag were determined to be 1500 °C, 14 wt% C, 20–25 wt% CaO, and 60–80 min. The recovery rates of iron and copper reached about 90% and 85%, and the contents of iron and copper in alloy reached about 91–93 wt% and 5–7 wt%, respectively. The tailing was mainly composed of Ca3Si3O9, Ca(Mg,Al)(Si,Al)2O6, and SiO2, which could be used as a raw material for cement and pelletizing.

Alloys doi: 10.3390/alloys3030009

Authors: Nikki Stanford

This year, several hot topics have emerged in alloy research and design; we have collected a few of these in this feature paper collection for your enjoyment [...]

Alloys doi: 10.3390/alloys3020008

Authors: Junguang He Zhenfei Cheng Jiuba Wen Peiwu Tian Wuyun Feng Xiangyang Zheng Yuan Gong

In this investigation, the effects of different annealing temperatures (180, 200, 220, 240, 260, and 280 °C) on the microstructure evolution and properties of an extruded Mg–2.0Zn–1.0Y–0.5Zr (wt%) magnesium alloys were determined. Optical microscopy (OM), scanning electron microscopy (SEM), immersion corrosion, electrochemical corrosion experiments, and tensile testing were performed. Research has found that combining hot extrusion with subsequent low-temperature annealing significantly improves the strength, plasticity, and corrosion resistance of alloys due to grain refinement and a reduced dislocation density. The alloy was completely recrystallized at an annealing temperature of 240 °C for 4 h after solid solution extrusion, and the grains were fine and uniform, demonstrating the best comprehensive properties. Its corrosion rate, ultimate tensile strength, yield strength, and elongation were 0.454 ± 0.023 mm/y, 346.7 ± 8.9 MPa, 292.4 ± 6.9 MPa, and 19.0 ± 0.4%, respectively. The corrosion mechanism of the specimens under extruded and annealed conditions was analyzed. After annealing at 240 °C for 4 h, the dislocation and bimodal grain structure of the samples were almost eliminated, resulting in uniform and fine grains, which were conducive to the formation of a more uniform and denser oxide film, thus improving the corrosion resistance of the alloy.

Alloys doi: 10.3390/alloys3020007

Authors: Bhila Mnisi Moseti Benecha Malebo Tibane

Transition metal-ruthenium alloys are promising candidates for ultra-high-temperature structural applications. However, the mechanical and electronic characteristics of these alloys are not well understood in the literature. This study uses first-principles density functional theory calculations to explore the structural, electronic, mechanical, and phonon properties of X3Ru (X = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn) binary alloys in the tP16 crystallographic phase. We find that Mn3Ru, Sc3Ru, Ti3Ru, V3Ru, and Zn3Ru have negative heats of formation and hence are thermodynamically stable. Mechanical analysis (Cij) indicates that all tP16-X3Ru alloys are mechanically stable except, Fe3Ru and Cr3Ru. Moreover, these compounds exhibit ductility and possess high melting temperatures. Furthermore, phonon dispersion curves indicate that Cr3Ru, Co3Ru, Ni3Ru, and Cu3Ru are dynamically stable, while the electronic density of states reveals all the X3Ru alloys are metallic, with a significant overlap between the valence and conduction bands at the Fermi energy. These findings offer insights into the novel properties of the tP16 X3Ru intermetallic alloys for the exploration of high-temperature structural applications.

Alloys doi: 10.3390/alloys3010006

Authors: Bobo Lu Kai Tang Mingxia Wu Yi Yang Gang Yang

Residual stress is caused by non–uniform deformation caused by non–uniform force, heat and composition, which is of great significance in engineering applications. It is assumed that the residual stress is always the upper limit of the elastic limit, so the reduction of the flow stress will reduce the residual elastic stress. It is particularly important to control the flow stress in metal materials. Compared with traditional methods, the use of electropulsing treatment (EPT) technology stands out due to its energy–efficient, highly effective, straightforward and pollution–free characteristics. However, there are different opinions about the mechanism of reducing flow stress through EPT due to the conflation of the effects from pulsed currents. Herein, a clear correlation is identified between induced stress levels and the application of pulsed electrical current. It was found that the decrease in flow stress is positively correlated with the current density and the duration of electrical contact and current action time. We first systematically and comprehensively summarize the influence mechanisms of EPT on dislocations, phase, textures and recrystallization. An analysis of Joule heating, electron wind effect, and thermal–induced stress within metal frameworks under the influence of pulsed currents was conducted. And the distribution of electric, thermal and stress fields under EPT are discussed in detail based on a finite element simulation (FES). Finally, some new insights into the issues and challenges of flow stress drops caused by EPT are proposed, which is critically important for advancing related mechanism research and the revision of theories and models.

Alloys doi: 10.3390/alloys3010005

Authors: Nik Tankov Claire Utton Panos Tsakiropoulos

In this work, the refractory complex concentrated alloy (RCCA) 3.5Al–4Cr–6Ge–1Hf–5Mo–36Nb–22Si–1.5Sn–20Ti–1W (at.%) was studied in the as cast and heat treated conditions (100 h or 200 h at 1500 °C). There was strong macrosegregation of Si in the 0.6 kg button/ingot of the cast alloy, in which A2 solid solution, D8m βNb5Si3, C14-NbCr2 Laves phase and Tiss and a ternary eutectic of the A2, D8m and C14 phases were formed. The partitioning of Ti in the as cast and heat treated microstructure and its relationships with other solutes was shown to be important for the properties of the A2 solid solution and the D8m βNb5Si3, which were the stable phases at 1500 °C. The near surface microstructure of the alloy was contaminated with oxygen after heat treatment under flowing Ar. For the aforementioned phases, it was shown, for the first time, that there are relationships between solutes, between solutes and the parameters VEC, Δχ and δ, between the said parameters, and between parameters and phase properties. For the contaminated with oxygen solid solution and silicide, trends in relationships between solutes, between solutes and oxygen content and between the aforementioned parameters and oxygen content also were shown for the first time. The nano-hardness and Young’s modulus of the A2 solid solution and the D8m βNb5Si3 of the as cast and heat-treated alloy were measured using nanoindentation. Changes of nano-hardness and Young’s modulus of the A2 solid solution and D8m βNb5Si3 per solute addition for this multiphase RCCA were discussed. The nano-hardness and Young’s modulus of the solid solution and the βNb5Si3, respectively, were 9.5 ± 0.2 GPa and 177.4 ± 5.5 GPa, and 17.55 ± 0.5 GPa and 250.27 ± 6.3 GPa after 200 h at 1500 °C. The aforementioned relationships and properties of the two phases demonstrated the importance of synergy and entanglement of solutes, parameters and phases in the microstructure and properties of the RCCA. Implications of synergy and entanglement for the design of metallic ultra-high temperature materials were emphasised.

Alloys doi: 10.3390/alloys3010004

Authors: Lamiaa Z. Mohamed Sanaa S. Abd ElMoamen Seung Jo Yoo Mohamed Abdel-Hady Gepreel

The isothermal oxidation of a Fe35Mn21Ni20Cr12Al12 high entropy alloy (HEA) was investigated in dry air for 50 h at 500, 600, and 700 °C after 90% cold rolling. The Fe35Mn21Ni20Cr12Al12 HEA behaves according to the linear oxidation rate with rate constants of 1 × 10−6, 3 × 10−6, and 7 × 10−6 g/(cm2·s) for oxidation at 500 °C, 600 °C, and 700 °C, respectively. The activation energy for oxidation of the HEA was calculated to be 60.866 KJ/mole in the 500–700 °C temperature range. The surface morphology and phase identification of the oxide layers were characterized. The formation of MnO2, Mn2O3, Mn3O4, Cr2O3, and Al2O3 in the oxide layers along with Fe2O3 is the key to the oxidation mechanism. The elemental mapping and line EDX scans were performed to identify the oxidation mechanisms.

Alloys doi: 10.3390/alloys3010003

Authors: Hans-Christian Weissker Florent Calvo

Gold and silver are, for all their chemical similarities, optically very different. Small Ag clusters show a localized surface-plasmon resonance (LSPR), whereas in Au clusters smaller than about 300 atoms, the resonance is absent due to the coupling with the interband transitions from the d electrons. This opens the possibility of tuning the cluster properties depending on their composition and chemical configuration. Earlier work on AgAu alloy clusters has shown that the outermost shell of atoms is crucial to their overall optical properties. In the present contribution, we consider the optical spectroscopic properties associated with the structural rearrangement in 55-atom AgAu alloy clusters in which the core transforms from pure silver to pure gold. Calculations using time-dependent density-functional theory are complemented by an in-depth study of the subtle effects that the chemical configuration has on the details of the materials’ d bands. Although the cluster surface remains alloyed, the geometrical changes translate into strong variations in the optical properties.

Alloys doi: 10.3390/alloys3010002

Authors: Tshegofatso Phaahla Phuti Ngoepe Hasani Chauke

Bimetallic nanoclusters have attracted great interest due to their ability to enhance the catalytic properties of nanoclusters through synergetic effects that emerge from the combination of the metal nanocluster with different transition metal (TM) species. However, their indefinite composition and broad distribution hinder the insightful understanding of the interaction between these invasive metals in bimetallic doped nanoalloys. In this study, we report a density functional theory calculation with the PBEsol exchange-correlation functional for 16-atom TiN−1TM (TM = Ni, Ir, Pd) nanoalloys, which provides new insights into the synergetic effect of these invasive metals. The probe into the effect of these metal impurities revealed that the replacement of a Ti atom with Ni, Ir and Pd enhances the relative stability of the nanoalloys, and the maximum stability for a lower bimetallic composition is reached for Ti4Ir, Ti5Pd and Ti7Ni. The most stable nanoalloy is reached for the Ti12Ir cluster in comparison with the Ti12Pd and Ti12Ni clusters and pure Ti13 monoatomic nanocluster. This stability trend is as revealed well by both the binding energy and the dissociation energy. The average HOMO-LUMO gap for the bigger clusters revealed that the valence electrons in the HOMO can absorb lower energy, which is indicatory of a higher reactivity and lower stability. The quantum confinement is higher for the smaller clusters, which illustrates a higher stability and lower reactivity for those systems.

Alloys doi: 10.3390/alloys3010001

Authors: Renee Erica Gordon Egwu Eric Kalu Adelana Rasak Adetunji Dorr Campbell Peter N. Kalu

As part of a comprehensive study on eco-friendly processing techniques, the influence of the heat treatment environment on the case hardening of AISI 1018 steel using pulverized cassava leaf was studied. The process was carried out at two different temperatures (850 °C and 950 °C) and under three environmental conditions: Process 1, the control experiment, was carried out in air only; in Process 2, the medium comprised pulverized cassava leaves; and in Process 3 a combination of pulverized cassava leaves plus barium carbonate (BaCO3) was used as an energizer (CBC mixture). Vickers microhardness testing and scanning electron microscopy were used to evaluate the effect of the processing environment on the case hardening of the steel. As expected, regardless of the processing temperature, Process 1 resulted in little or no hardening of the steel surface. However, notable case hardening occurred when the steel specimens were subjected to either Process 2 or Process 3. Furthermore, the inclusion of barium carbonate in Process 3 significantly enhanced the case hardening effectiveness of the cassava leaf in terms of the rate of and maximum hardness achieved. A maximum enhancement was observed at 950 °C. After 1 h, the increase in hardness was 160% and 280% for Process 2 and Process 3, respectively. Upon increasing the processing time to 5 h, the increase in hardness due to Process 2 was raised to 254%, while that of Process 3 remained at approximately 280%. The diffusivity of AISI 1018 was calculated using the microhardness data. The diffusivity was highest in Process 2 samples with values of 1.568 × 10−9 m2/s at 850 °C and 1.893 × 10−9 m2/s at 950 °C. Effective case hardening of AISI 1018 steel was carried out using the medium of cassava leaf, without the addition of barium carbonate (BaCO3) as an energizer.

Alloys doi: 10.3390/alloys2040021

Authors: Chunhui Luo Karin Hansson Zhili Song Debbie Ågren Ewa Sjöqvist Persson Fredrik Cederholm Changji Xuan

Integrated computational materials engineering (ICME) is emerging as an increasingly powerful approach to integrate computational materials science tools into a holistic system and address the multiscale modeling challenges in the processing of advanced steels. This work aims at incorporating macroscopic model (finite element-based thermal model) and microscopic model (CALPHAD-based microstructure model), building an industry-oriented computational tool (MICAST) for casting of steels. Two case studies were performed for solidification simulations of tool steel and stainless steel by using the CALPHAD approach (Thermo-Calc package and CALPHAD database). The predicted microsegregation results agree with the measured ones. In addition, two case studies were performed for continuous casting and ingot casting with selected steel grades, mold geometries and process conditions. The temperature distributions and histories in continuous casting and ingot casting process of steels were calculated using in-house finite-element code which is integrated in MICAST. The predicted temperature history from the casting process simulation was exported as input data for the DICTRA simulation of solidification. The resulting microsegregation by the DICTRA simulation can reflect the microstructure evolution in the real casting process. Current computational practice demonstrates that CALPHAD-based material models can be directly linked with casting process models to predict location-specific microstructures for smart material processing.

Alloys doi: 10.3390/alloys2040020

Authors: Oliver Hentschel Jan Kohlstruck Pavel Krakhmalev Dimitrios Nikas Michael Schmidt

A promising approach for producing parts with outstanding properties in directed energy deposition (DED-LB/M) provides the application of tailored powder mixtures processed by applying in situ alloying strategies. In this work, DED-LB/M was used to manufacture multilayer specimens from AISI H11 steel powders enriched with carbon nanoparticles (C-np) in concentrations of 0.1 wt.-% and 0.2 wt.-%. The scientific aim was to investigate the impact of C-np on the microstructural (particularly retained austenite content (RA-c) and grain size) and mechanical properties (specifically hardness and compression yield strength) of the manufactured specimens. It was shown that the addition of C-np to the H11 powder leads to a stronger distortion of martensite as well as significantly enhancing the RA-c. Furthermore, the C-np seem to favor the formation of finer martensite, as can be verified with XRD and EBSD. Under as-built conditions, the mean hardness increases from 653 ± 10 HV1 for the H11 sample to 770 ± 14 HV1 for the sample reinforced with 0.2 wt.-% C-np. At the same time, Y0.2% rises up from 1839 ± 61 MPa to 2134 ± 68 MPa. The hardness- and strength-increasing effect of the added C-np is retained even after heat treatment, similarly to the industrial standard.

Alloys doi: 10.3390/alloys2040019

Authors: Yingbo Zhang Yuanhui Peng Pu Zhang Yunfeng Hu Dongliang Wu Xing Tu

This article presents a novel and feasible approach for researching the quantity of the ceramic phase and component optimization in high-temperature titanium alloys with small trace amounts of ceramic phases. Different near-α titanium alloys with varying yttrium and boron contents were prepared through the utilization of a vacuum non-consumable arc furnace melting method. The alloy used was a Ti-5.9Al-4Sn-3.9Zr-3.8Mo-0.4Si base. Its microstructure, texture, mechanical properties, and fracture behavior were studied. The observation of the as-cast structure shows that the addition of different doses of trace Y and B elements significantly refines both the original β grains and α grains. Moreover, the addition of the B element transforms the Widmanstätten structure in the titanium alloy structure into a basketweave structure. The addition of Y can refine the grain structure, improve the uniformity of the matrix structure, and act as a strong deoxidizer, which will take away the oxygen in the matrix and purify it. The TiB whiskers generated with the addition of B promotes dynamic recrystallization behavior and leads to more equiaxed α grains being precipitated around them, resulting in a significant refinement of the microstructure of the as-cast alloy. After adding a small amount of B, the texture strength of the α phase is significantly reduced, indicating that TiB whiskers inhibit the formation of texture. After conducting performance screening and structure analysis, the study supplements the analysis of Y’s regulation of the titanium alloy structure. The regulation is primarily explained by combining the results of the analysis of boron content, phase diagram analysis, mechanical properties, and fracture analysis. The mechanical analysis introduces the unique load transfer strengthening of TiB whiskers combined with an analysis of high-temperature mechanical properties, as the threshold for addition. The optimal amounts of Y and B additions are 0.6 wt% and 0.8 wt%, respectively. The optimized alloy obtained under this condition can achieve a tensile strength of 950 Mpa at 500 °C without any plastic deformation or heat treatment.

Alloys doi: 10.3390/alloys2040018

Authors: Wei Liu Zhenchao Zhang Suli Li Chao Xu

Ultrasonic-assisted Ti6Al4V Directed Energy Deposition (DED) additive manufacturing technology can improve the problem of uneven microstructure caused by laser heating and sudden cooling of the molten pool. In this paper, the numerical analysis and experimental verification methods were adopted. The influencing factors, such as the cavitations’ effect, sound flow enhancement effect, and sound flow thermal effect related to the ultrasonic assistance in the molten pool, were analyzed. After equating the energy of the ultrasound, the model of additive manufacturing was introduced in the form of a heat source. The temperature gradient changes during the solidification process of the molten pool with the addition of ultrasound assistance and the effect of ultrasonic vibration during the manufacturing process on its deposited state and microstructure of solution-aged formed parts were studied. The results showed that when the wire feeding rate is 5 mm/s and the laser scanning speed is 5 mm/s, the optimal laser power is 1000 W~1100 W, corresponding to the optimal ultrasonic amplitude of 120 μm. Then, by comparing the temperature field with the same amplitude of 0 μm (i.e., no ultrasonic vibration) and the microstructure of the formed parts, it was verified that ultrasonic vibration facilitates fluid flow in the molten pool, which could lead to a more uniform temperature distribution. This optimized approach not only enhances the understanding of the process but also contributes significantly to the advancement of related research endeavors.

Alloys doi: 10.3390/alloys2040017

Authors: Alexander S. Dedyukhin Andrey V. Shchetinskiy Vladimir A. Volkovich Leonid F. Yamschchikov

The solubility of lanthanum in indium and Ga–In alloys containing 21.8, 40 and 70 wt. % In was determined experimentally at temperatures up to 1081 K. The low temperature limit depended on the melting point of the alloy. The solubility was measured using isothermal saturation and high-temperature filtration methods. The phase composition of solid intermetallic compounds formed in the ternary La–Ga–In systems of various compositions was determined by X-ray diffraction. Activity coefficients of lanthanum in the alloys based on gallium, indium and three Ga–In mixtures (21.8, 40 and 70 wt. % In) were calculated. Temperature dependencies of thermodynamically possible separation factors for the uranium/lanthanum couple in “LiCl–KCl–CsCl melt–liquid alloy” systems were derived for various gallium–indium alloys.

Alloys doi: 10.3390/alloys2040016

Authors: Xin Liu Shen Li Hui Wang Menghe Tu Bokai Zhou Yong Hu

In pressurized water reactors (PWRs), flow-induced vibration (FIV) induces the fretting wear of fuel rods and supporting grids, and the process is accompanied by corrosion, which is called fretting corrosion. In this paper, fretting corrosion experiments were carried out in a simulated cladding service environment, and the fretting corrosion performance of AlCrNbSiTi coating cladding, Cr coating cladding and uncoated cladding with the supporting grids were investigated using a three-dimensional white light interferometer and a scanning electron microscope (SEM). The results showed that the AlCrNbSiTi coating cladding has the strongest fretting corrosion performance, the Cr coating cladding has the second best fretting corrosion performance and the uncoated cladding has the worst fretting corrosion performance. The coating also changes the wear mechanism of the cladding and improves the corrosion resistance of the cladding, which is responsible for the improvement in the fretting corrosion performance of the cladding. By comparing the AlCrNbSiTi coating with the Cr coating, it was found that the AlCrNbSiTi coating has a better fretting corrosion performance than the Cr coating due to its higher hardness and stronger corrosion resistance.

Alloys doi: 10.3390/alloys2030015

Authors: Kipkorir Kirui Pius Nicholas O. Ongwen Maxwell Mageto Victor Odari Francis Magiri Gaitho

Al–Mg–Si alloys are used in aircraft, train, and car manufacturing industries due to their advantages, which include non-corrosivity, low density, relatively low cost, high thermal and electrical conductivity, formability, and weldability. This study investigates the bulk mechanical properties of Al–Mg–Si alloys and the influence of the Si/Mg ratio on these properties. The Al cell was used as the starting structure, and then nine structures were modeled with varying percentages of aluminium, magnesium, and silicon. Elastic constant calculations were conducted using the stress–strain method as implemented in the quantum espresso code. This study found that the optimum properties obtained were a density of 2.762 g/cm3, a bulk modulus of 83.3 GPa, a shear modulus of 34.4 GPa, a Vickers hardness of 2.79 GPa, a Poisson’s ratio of 0.413, a Pugh’s ratio of 5.42, and a yield strength of 8.38 GPa. The optimum Si/Mg ratio was found to be 4.5 for most of the mechanical properties. The study successfully established that the Si/Mg ratio is a critical factor when dealing with the mechanical properties of the Al–Mg–Si alloys. The alloys with the optimum Si/Mg ratio can be used for industrial applications such as plane skins and mining equipment where these properties are required.

Alloys doi: 10.3390/alloys2030014

Authors: Panos Tsakiropoulos

The paper is a personal perspective on the design of metallic ultra-high temperature materials (UHTMs). Specifically, the alloy design “landscape” of metallic UHTMs was considered from the viewpoint of the alloy design methodology NICE. The concepts of synergy, entanglement and self-regulation and their significance for alloy design/development were discussed. The risks, ecological challenges and material-environment interactions associated with the development of metallic UHTMs were highlighted. The “landscape” showed that beneath the complexities of alloy design lies an elegant and powerful unity of specific parameters that link logically and that progress can be made by recognising those interrelationships between parameters that generate interesting, diverse, and complex alloys.

Alloys doi: 10.3390/alloys2030013

Authors: Dominic Bartels Moritz Elias Albert Florian Nahr Michael Schmidt

Case-hardening steels are gaining increasing interest in the field of laser powder bed fusion (PBF-LB/M) due to their excellent weldability. In combination with post-process carburization heat treatment, the surface properties can be improved to generate high-strength products. When manufacturing larger products by means of PBF-LB/M, the in situ heat accumulation and the altered cooling rates affect the resulting material properties. Therefore, the fabrication of larger products requires an understanding on the influencing factors that affect the material properties. This work investigates the effect of different volumetric energy densities (VED) on the resulting microstructural and mechanical properties. It is found that the hardness decreases continuously along the build direction. The gradient depends on the applied energy and is stronger for higher energy inputs due to heat accumulation and lowered cooling rates. Furthermore, countering strategies are investigated to avoid process-specific hardness reduction along the build direction. This includes a reduced number of parts within the build job as well as a modified inter-layer time (ILT) between consecutive layers of the specimen. Applying a moderate inter-layer time helps to counter process-specific overheating, which is indicated by an almost homogeneous material hardness and melt pool size along the build direction.

Alloys doi: 10.3390/alloys2030012

Authors: Anatoly Mukhachev Dmytro Yelatontsev Olena Kharytonova

This article presents the results of studies of the self-propagating high-temperature synthesis (SHS) for obtaining zirconium alloys with niobium by the method of calcium-thermal reduction of nuclear-grade zirconium tetrafluoride in the presence of niobium powder. The optimal heating temperature of the initial charge and the methods of charge mixture with different calcium content were determined. The safety of the SHS process is ensured by the formation of an optimal combustion front of the mixture to remove the released high-pressure gases. A setup for the furnace reduction of zirconium alloys with charge preheating, discharge of molten products into molds of various designs, and control of the time and rate of slag and alloy crystallization has been tested. The required performance of the installation, the degree of transition of zirconium from salt into the alloy, and the purity, structure, and uniformity of the alloy were achieved.

Alloys doi: 10.3390/alloys2030011

Authors: Arkadiy V. Dobromyslov

A systematic study of the phase composition of quenched binary titanium alloys with d-metals of groups 5–11 from periods four to six was carried out using the methods of X-ray diffraction analysis. It was found that the formation of the orthorhombic α″-phase depends on the position of the alloying metal in the periodic table. The formation of the α″-phase occurs only in the systems Ti-V, Ti-Nb, Ti-Mo, Ti-Ru, Ti-Ta, Ti-W, Ti-Re, Ti-Os and Ti-Ir, and in other systems, it does not occur. It was found that the critical parameter for the formation of the α″-phase is the difference in the size of titanium atoms and those of the alloying metal {(rTi − rMe)/rTi 100%}. The formation of the α″-phase occurs only in systems where this value is lower than 9 at.%.

Alloys doi: 10.3390/alloys2030010

Authors: Joerg Volpp Himani Naesstroem Lisanne Wockenfuss Malte Schmidt Knut Partes

Laser materials processing includes rapid heating to possibly high temperatures and rapid cooling of the illuminated materials. The material reactions can show significant deviations from equilibrium processing. During processing of complex materials and material combinations, it is mainly unknown how the materials react and mix. However, it is important to know which chemical elements or compounds are present in the material to define the alloy. In addition, their distribution after rapid cooling needs to be better understood. Therefore, such alloy changes at rapid heating induced by laser illumination were created as pre-placed and pre-mixed powder nuggets. The energy input and the material ratio between the powder components were varied to identify characteristic responses. For the detection of reaction durations and mixing characteristics, the vapor plume content was assumed to contain the necessary information. Spectral measurements of the plume were used to identify indicators about process behaviors. It was seen that the spectral data give indications about the chemical reactions in the melt pool. The reactions of iron ore components with aluminum seem to require laser illumination to finish completely, although the thermite reaction should maintain the chemical reaction, likely due to the required melt mixing that enables the interaction of the reacting partners at all.

Alloys doi: 10.3390/alloys2030009

Authors: Mark Petrov

Instead of a number of different approaches or a formal description of experimental data, a unified approach is proposed to consider failure and deformation as thermodynamic processes. Mathematical modeling of the processes is carried out using rheological models of the material. Parametric identification of structural models is carried out using minimal necessary experiments. Based on results of these experiments, the scope of applicability conditions for this material and test modes necessary for parametric identification of models are selected. One fracture criterion is used that formally corresponds to the achievement of a threshold concentration of micro-damage in any volume of the material. Calculations of durability under conditions of varying temperature and variable loads are based on the relationship of plastic flow and failure processes distributed over the volume of the material. They are performed numerically over time steps depending on the ratio of the rate of change of temperature and stresses.

Alloys doi: 10.3390/alloys2020008

Authors: Sofia Salles Lantyer Marques Rita de Cássia Mendonça Sales-Contini Jorge Otubo Heide Heloise Bernardi

In this work, the influence of heat treatment on the corrosion resistance of shape memory stainless steel based on FeMnSiCrNiCo was evaluated. Deformed samples were annealed from 250 °C to 1050 °C for 1 h. Scanning electron microscopy (SEM-EDS) and a Vickers microhardness test were used to characterize the microstructure. Thermal analysis was performed to identify phase transformations. Corrosion resistance was evaluated in an electrochemical test in a 3.5% NaCl solution. FeMnSiCrNiCo in the deformed state had better corrosion resistance compared to other conditions. However, as the annealing temperature increased, the corrosion resistance decreased due to the formation of precipitates.

Alloys doi: 10.3390/alloys2020007

Authors: Victor Pacheco Björn Skårman Fredrik Olsson Dennis Karlsson Hilmar Vidarsson Martin Sahlberg

Permanent magnets are becoming more and more relevant for modern society. As the most widely used permanent magnets contain rare-earth elements, the increased dependence on these strategic elements is worrisome, and the pursuit for rare-earth free alternatives has become a strategic goal in many countries. The metastable and ferromagnetic τ-phase that forms in the MnAl(C) system is one of the most promising alternatives, and since its discovery, major efforts have been made to improve its performance and realize its full potential. One major factor that has prevented a widespread commercialization of MnAl(C) permanent magnets is their relatively low coercivity. Here, we demonstrate that additive manufacturing, using laser powder bed fusion, can be used to produce MnAl in its high-temperature polymorph (ε, hcp), which can be subsequently transformed, through post-heat treatments to the ferromagnetic τ-phase. Although we successfully obtained a preferential orientation of the ε-phase with <001> parallel to the build direction, this did not translate into a strong preferential orientation in the τ-phase, thus indicating that the phase transformation occurs by the migration of incoherent interfaces. The MnAl(C) samples are characterized by a density of ≈4.4 g/cm3, a saturation magnetization of 39.3 Am2/kg, a coercivity of 168 kA/m, and a remanence of 17.5 Am2/kg.

Alloys doi: 10.3390/alloys2020006

Authors: Yuehua Sun Fan Zhang Jian Ren Guangsheng Song

The microstructure and mechanical properties of as-homogenized Mg-xLi-3Al-2Zn-0.2Zr alloys (x = 5, 7, 8, 9, 11 wt.%) were studied. As the Li content increased from 5 wt.% to 11 wt.%, the alloy matrix changed from the α-Mg single-phase to α-Mg+β-Li dual-phase and then to the β-Li single-phase. Homogenized With the increase in Li content, the alloy strength decreased while the elongation increased, and the corresponding fracture mechanism changed from cleavage fracture to microvoid coalescence fracture. This is mainly attributed to the matrix changing from α-Mg with hcp structure to β-Li with bcc structure. Additionally, the increase in the AlLi softening phase led to the reduction of Al and Zn dissolved in the alloy matrix with increasing Li content, which is one of the reasons for the decrease in alloy strength.

Alloys doi: 10.3390/alloys2010005

Authors: Sepehr Yazdani Veronique Vitry

The grain boundaries and dislocations play an important role in understanding the deformation behavior in polycrystalline materials. In this paper, the deformation mechanism of Cu, Ni, and equimolar Cu-Ni alloy was investigated using molecular dynamic simulation. The interaction between dislocations and grain boundary motion during the deformation was monitored using the dislocation extraction algorithm. Moreover, the effect of stacking fault formation and atomic band structure on the deformation behavior was discussed. Results indicate that dislocations nucleate around the grain boundary in copper, the deformation in nickel changes from planar slip bands to wavy bands, and high density of dislocation accumulation as well as numerous kink and jog formations were observed for the equimolar Cu-Ni alloy. The highest density of the Shockley dislocation and stacking faults was formed in the equimolar Cu-Ni alloy which results in the appearance of a huge gliding stage in the stress–strain curve. The grain boundaries act as a sinking source for vacancy annihilation in Ni and Cu; however, this effect was not observed in an equimolar Cu-Ni alloy. Finally, radial distribution function was used to evaluate atom segregation in grain boundaries.

Alloys doi: 10.3390/alloys2010004

Authors: Harry O. Psihoyos George N. Lampeas

One of the main challenges encountered in the Laser-based Powder Bed Fusion (L-PBF) Additive Manufacturing (AM) process is the fabrication of defect-free parts. The presence of defects severely degrades the mechanical performance of AM parts and especially their fatigue strength. The most popular and reliable method to assess the ability of the employed process parameters for the fabrication of full-density parts is the process windows map, also known as printability map. However, the experimental procedure for the design of the printability maps and the identification of the optimum-density process parameters is usually time-consuming and expensive. In the present work, a modelling framework is presented for the determination of a printability map and the optimization of the L-PBF process based on the prediction and characterization of melt-pool geometric features and the prediction of porosity of small samples of 316L SS and Ti-6Al-4V metal alloys. The results are compared with available experimental data and present a good correlation, verifying the modelling methodology. The suitability of the employed defect criteria for each material and the effect of the hatch-spacing process parameter on the optimum-density parameters are also presented.

Alloys doi: 10.3390/alloys2010003

Authors: Tomasz Stasiak Mourtada Aly Sow Matthieu Touzin Franck Béclin Catherine Cordier

High entropy alloys present many promising properties, such as high hardness or thermal stability, and can be candidates for many applications. Powder metallurgy techniques enable the production of bulk alloys with fine microstructures. This study aimed to investigate powder metallurgy preparation, i.e., mechanical alloying and sintering, non-equiatomic high entropy alloy from the Al-Cr-Fe-Mn-Mo system. The structural and microstructural investigations were performed on powders and the bulk sample. The indentation was carried out on the bulk sample. The mechanically alloyed powder consists of two bcc phases, one of which is significantly predominant. The annealed powder and the sample sintered at 950 °C for 1 h consist of a predominantly bcc phase (71 ± 2 vol.%), an intermetallic χ phase (26 ± 2 vol.%), and a small volume fraction of multielement carbides—M6C and M23C6. The presence of carbides results from carbon contamination from the balls and vial during mechanical alloying and the graphite die during sintering. The density of the sintered sample is 6.71 g/cm3 (98.4% relative density). The alloy presents a very high hardness of 948 ± 34 HV1N and Young’s modulus of 245 ± 8 GPa. This study showed the possibility of preparing ultra-hard multicomponent material reinforced by the intermetallic χ phase. The research on this system presented new knowledge on phase formation in multicomponent systems. Moreover, strengthening the solid solution matrix via hard intermetallic phases could be interesting for many industrial applications.

Alloys doi: 10.3390/alloys2010002

Authors: Pedro A. Ferreirós Abraham A. Becerra Uriel A. Sterin Martina C. Ávalos Raúl E. Bolmaro Gerardo H. Rubiolo

Nowadays, great efforts are being made to develop bcc-superalloys for medium- and high-temperature applications. However, the high brittle-to-ductile transition temperatures (BDTT) have restricted their application. Therefore, designing hot-processing routes to obtain a refined grain in these new superalloys is required. Particularly in the Fe-10Al-12V (at%) alloy, we have recently tested the BDTT shifting and, using physical models, it was indicated that a combination of L21-precipitate sizes with small grain sizes could shift the BDTT below room temperature. Here, we will present the study that allowed us to design the processing route for grain refinement in the tested superalloy. Molds of different geometry and with metallic and sand walls were used to test two different types of casting. Carbide conditioning treatments for improving the sizes and distribution were studied. The recrystallization process was explored first by hot rolling and post-annealing in stepped geometry samples with two different columnar grain orientations. Finally, we analyzed the grain microstructure obtained along a hot processing route consisting of carbide conditioning treatment, forging into a squared bar, and hot rolling up to a 2.8 mm thickness strip.

Alloys doi: 10.3390/alloys2010001

Authors: Hardy Mohrbacher Andreas Kern

Nickel is an important and widely used alloying element in carbon steels. Some of its prominent metallurgical effects in these steels are moderate solid solution strengthening, mild hardenability and, importantly, a strong promotion of toughness, especially at low temperatures. The first uses of nickel as an alloying element in commercial steel production date back to the early 20th century. The aim of the current review is to give the reader a thorough and concise overview of nickel functionalities relevant to modern carbon steel production. The interaction of nickel with other alloying elements and processing conditions is also considered. Examples will be given demonstrating the advantages of nickel alloying in selected steel grades and applications.

Alloys doi: 10.3390/alloys1030019

Authors: Christoph Priese Jörg Töpfer

FeSiCr alloys are used as soft magnetic materials for power multilayer inductors. The alloys are typically annealed at intermediate temperatures in air during inductor fabrication to form an insulating chromium oxide layer around the alloy particles. The variation of the annealing temperature between 700 °C and 900 °C in air, and, for the first time, the variation of the oxygen partial pressure during annealing at 900 °C are studied, and their effects on the alloy’s oxidation behavior, phase formation, insulation resistance, and permeability are demonstrated. The chromium oxide content increases up to about 12 wt% with annealing temperature in air, whereas it decreases to 8.2 wt% after annealing at 900 °C and 0.001% O2. The observed mass changes during annealing confirm the various tendencies towards oxidation. This oxidation behavior is reflected in an increase in the insulation resistance with annealing temperature or in a resistance reduction with decreasing oxygen partial pressure. The permeability decreases from µ = 22 after annealing at 700 °C to µ = 18.5 at 900 °C in air. The reduction of pO2 during annealing at 900 °C leads to an increase in permeability up to µ = 22.5 at pO2 = 0.001% O2. The results can be used to design cofiring strategies using reduced oxygen partial pressure for new composite multilayer inductive components consisting of FeSiCr- and ferrite layers in combination with silver metallization.

Alloys doi: 10.3390/alloys1030018

Authors: Kirstin Riener Alexander Nagler Ilse Letofsky-Papst Gerhard Leichtfried

The demand for high-strength aluminum alloys for the laser powder bed fusion (LPBF) process is still growing. However, to date, the crack susceptibility of conventional alloys as well as the high prices for specially developed alloys are the main obstacles for the use of high-strength aluminum alloys for LPBF. In this paper, crack-free LPBF samples with a relative density >99.9% were processed from AlMgSi1Zr (6182 series alloy) powder, to which 0.5 wt.-% Zr and 0.5 wt.-% Ti were added via mechanical mixing. No hot cracks were found in the µCT scans. Moreover, a fully equiaxed microstructure with a mean size of the α-Al grains of 1.2 µm was observed in the as-built parts. Al3(Zr,Ti) particles were observed, acting as efficient heterogeneous grain refiners for α-Al by building a semi-coherent interface. Unmolten Ti and Zr particles with sizes up to 80 µm were found in the α-Al phase. The resulting fine-grained microstructure led to a tensile strength of 329 ± 4 MPa and a total elongation at a break of 11.4 ± 0.9% after solution heat treatment, quenching in water, and subsequent artificial ageing.

Alloys doi: 10.3390/alloys1030017

Authors: Dennis Karlsson Thomas Helander Eleonora Bettini Carl-Johan Hassila Johan Cedervall Martin Sahlberg Peter Harlin Ulf Jansson

Additive manufacturing (AM) techniques such as laser powder bed fusion (L-PBF) are rapidly growing due to the inherent design freedom and possibilities to produce components not available with other techniques. This could be utilized in, e.g., the design of new types of heat exchangers in ferritic stainless steels often used for high-temperature applications. Ferritic stainless steels are, however, difficult to weld and could therefore imply obstacles when produced by AM. When establishing the AM-produced alloy in new applications, it is therefore important to increase the understanding of the mechanical properties and high-temperature creep resistance in relation to the unique microstructure and printability. In this study, we have investigated the microstructure of Cr-rich SS446 ferritic stainless steel produced by L-PBF by microscopical and crystallographic techniques. The properties were compared to the conventionally produced tubes. The rapid cooling and reheating during the application of the subsequent powder layers during L-PBF introduces an intriguing microstructure consisting of a ferritic matrix with precipitation of austenite showing a Kurdjumov–Sachs orientation relationship. Characteristic dislocation networks were observed in the L-PBF samples and contributed to the good mechanical properties in the as-built state (more than twice the yield strength of the conventionally produced tube). Furthermore, the creep resistance at 800 °C was superior to the conventionally produced component, suggesting that L-PBF-produced SS446 possesses many advantages regarding production as compared to the conventional route.

Alloys doi: 10.3390/alloys1030016

Authors: Sunitha Raveendran Athul Kumar Arun Saktivel Swathi Uralath Dhanavardhanan Remya Andrea Dzubinska Marian Reiffers Ramamoorti Nagalakshmi

In this work, the structural, magnetic, thermal, and transport properties of the arc-melted polycrystalline Heusler alloy Co2Ti1.5Sn0.5 are investigated. The alloy crystallizes in an L21 structure with a space group of Fm-3m. The magnetic properties of the alloy depict its antiferromagnetic nature and the alloy exhibits magnetic ordering around Neel Temperature TN = 8.5 K. The effective magnetic moment value obtained from the Curie –Weiss law suggests that the cobalt atom in the alloy is in the low-spin state. From the heat capacity studies, the Sommerfeld coefficient and Debye temperature were determined. In addition, electrical resistivity shows a linear response with increasing temperature, indicating the metallic nature of the alloy.

Alloys doi: 10.3390/alloys1030015

Authors: Andreas Bezold Nicklas Volz Fei Xue Mathias Göken Steffen Neumeier

The defect evolution associated with an anomalous work hardening behavior of a single crystalline quaternary Co-Al-W-Ta superalloy at 950 °C was investigated by transmission electron microscopy. As plastic deformation is initially confined to the γ matrix channels, a plateau arises in the stress-strain curve after yielding. At about 1% plastic strain, extensive shearing of the γ′ precipitates under superlattice stacking fault formation occurs leading to extreme work hardening rates up to 12 GPa and a total increase in stress of about 200 MPa. Additional investigations on the temperature and strain-rate dependence of the anomalous work hardening behavior reveal the significance of diffusion and segregation processes on the stress-strain curve and the work hardening behavior.

Alloys doi: 10.3390/alloys1030014

Authors: Leandro Bolzoni Elisa Maria Ruiz-Navas Elena Gordo

Titanium alloys are ideal for a great range of engineering applications; however, their high manufacturing costs hinder their widespread use. This study investigates the relationship between the processing and properties of representative Ti-based materials manufactured via powder metallurgy in order to reduce the manufacturing costs. This is possible as powder metallurgy techniques are near-net shape processes with high yield of material. It is found that the relative density increases with the sintering temperature, and it is slightly higher for longer processing times, reaching values in the 94–97% range. Moreover, homogeneous microstructures are obtained for all the conditions investigated, achieving an equiaxed microstructure for Ti and the typical lamellar structure for the Ti-6Al-7Nb alloy. However, the increment of the temperature also leads to a higher amount of interstitial pick-up, with a maximum increment of 0.21 wt.% and 0.028 wt.% for oxygen and nitrogen, respectively. The highest properties achieved for Ti and Ti-6Al-7Nb are 272 HV (hardness), 17.9 W/m·K (thermal conductivity), and 62.7 μohm·cm (electrical resistivity) and 336 HV, 6.9 W/m·K, and 180 μohm·cm, respectively.

Alloys doi: 10.3390/alloys1020013

Authors: Yanqing Su M. Arul Kumar Irene J. Beyerlein

Application of polycrystalline hexagonal close packed (HCP) metals in engineering designs has been constrained by their anisotropic responses due to twinning and limited plasticity. In deformation, twins most often initiate at grain boundaries (GBs), and thicken and propagate across the grain. In this work, the GB twin embryos in Mg and Mg alloys, and the conditions that influence their propagation are investigated. Using a micromechanical crystal plasticity model, the role of embryo shape on the driving forces prevailing at the embryo boundaries that could support its expansion is studied. The modeled embryos are either planar, extending more in the shear direction than normal to the twin plane, or equiaxed. Results show that the thinner the embryo, the greater the driving forces for both thickening and forward propagation. Alloys with low prismatic-to-basal critical resolved shear stress (CRSS) ratios promote embryo thickening and large CRSS values for the slip mode that primarily accommodates the twin shear encourage propagation. The neighboring grains with orientations that enable local accommodation of the embryo twin shear by pyramidal slip promote forward propagation but have little effect on thickening. When two like embryos lie along the same GB, their paired interaction promotes forward propagation but hinders thickening.

Alloys doi: 10.3390/alloys1020012

Authors: Emilio Bassini Federico Simone Gobber Elisa Fracchia Chiara Zenaro Enrico Boccaleri

In this paper, a perfluoropolyether (PFPE) micellar solution was effectively deposited on metallic substrates using a dip-coating process to enhance brass and nickel aluminum bronze (NAB) corrosion resistance. Particular attention was paid to the aesthetic results as well. Enabling the metallic substrates hydrophobic to facilitate water and moisture removal was the key concept of this work. The corrosion resistance of the as-received and coated metals was investigated via a salt spray chamber test. The study focused on the characterization of the polymeric coating via dynamic light scattering and wettability tests, while the substrates were assessed with traditional metallographic techniques. The preparation of the polymeric solution was important in determining the final corrosion resistance of the two substrates. Noteworthy was the effectiveness of the PFPE-based coating when it was applied to the brass rather than the NAB. Moreover, the polymer concentration of the dip-coating polymeric emulsion was the most significant factor to obtaining adequate protection: higher polymer concentrations resulted in a decrease in corrosion resistance.

Alloys doi: 10.3390/alloys1020011

Authors: Nikolaos D. Alexopoulos Joseph D. Robson George Stefanou Vasileios Stergiou Alexandra Karanika Stavros K. Kourkoulis

The impact of the artificial aging response on the microstructure and tensile mechanical properties of aluminum alloy 6156 was investigated. Specimens were artificially aged at three different artificial aging temperatures and for various holding times to investigate all possible aging conditions, including the under-aged (UA), peak-aged (PA) and over-aged (OA) tempers. Microstructural investigation as well as tensile tests were performed immediately after the isothermal artificial aging heat treatment. An almost 50% increase in yield stress (around 340 MPa) was noticed in the PA temper and this was attributed to the precipitation of β′ and Q′ phases, consistent with the modelling predictions. This high yield stress value is accompanied by high values of elongation at fracture (>10%) that is essential for damage tolerance applications. The lack of large or interconnected grain boundary precipitates contributes to this high elongation. Slanted fracture was noticed for both UA and PA tempers, exhibiting a typical ductile and shear fracture mechanism. At the OA temper, coarsening of the precipitates along with broadening of the precipitate free zones resulted in a reduction in the strengthening effectiveness of the precipitates, and a small increase in the tensile ductility of approximately 12% was noticed.

Alloys doi: 10.3390/alloys1020010

Authors: Ritam Pal Amrita Basak

Additive manufacturing (AM) of metals can be broadly accomplished via two defined technologies: powder bed fusion and directed energy deposition. During AM fabrication, the melted feedstock material experiences fast thermal cycling due to the layer-by-layer deposition process resulting in microstructures and properties that are drastically different from the traditionally manufactured parts. For AM to become a viable process for fabricating critical components made of high-performance structural alloys, such as AlSi10Mg, a comprehensive understanding is required toward developing the process-structure-property relationships prevalent in AM. AlSi10Mg, with its good castability, strength, hardness, and dynamic properties, is typically used to fabricate structural components that are required to withstand high loads. This alloy has been consolidated predominantly by the laser powder bed fusion (L-PBF) method and several critical mechanical properties, such as fatigue, have been reported to date. This article, first, summarizes the as-deposited and heat-treated microstructures of AlSi10Mg specimens fabricated by L-PBF. Then, the article discusses the linkages among the feedstock properties, printing parameters, specimen geometry, post-processing techniques, and fatigue properties. This discussion is followed by a section on the fatigue life prediction of AlSi10Mg specimens using computational modeling. Finally, the article identifies critical research gaps and pinpoints future research opportunities.

Alloys doi: 10.3390/alloys1020009

Authors: Jacek Komenda Chunhui Luo Johan Lönnqvist

Varying contents of carbon, titanium and boron were used in the base steel composition of 0.30 wt% Si, 2.0 wt% Mn, 0.006 wt% S, 0.03 wt% Nb, and 30–35 ppm N. Hot ductility tests were performed with Gleeble-3800, after the steel sample was in-situ melted, solidified, and cooled to the test temperature. Investigation was completed with thermodynamic and kinetic simulations. The best results were obtained for steels containing 58–100 ppm B and 35 ppm Ti. They showed very good hot ductility of 80–50% RA within the temperature range between 1250 °C and 800 °C. It was shown that titanium and boron were effective in improving the hot ductility. Titanium protected boron from binding into BN and was low enough to prevent excessive (Ti,Nb) carbonitride precipitation, which both could decrease hot ductility. Boron that precipitated along austenite grain boundaries as iron boride Fe2B was very beneficial for the hot ductility of steel.

Alloys doi: 10.3390/alloys1020008

Authors: Shashanka Rajendrachari

Some modern alloys, such as high-entropy alloys (HEAs), are emerging with greater acceleration due to their wide range of properties and applications. HEAs can be prepared from many metallurgical operations, but mechanical alloying is considered to be one of the most simple, economical, popular, and suitable methods due to its increased solid solubility, nano-crystalline structure, greater homogeneity, and room-temperature processing. Mechanical alloying followed by the consolidation of HEAs is crucial in determining the various surface and mechanical properties. Generally, spark plasma sintering (SPS) methods are employed to consolidate HEAs due to their significant advantages over other conventional sintering methods. This is one of the best sintering methods to achieve greater improvements in their properties. This review discusses the mechanical alloying of various HEAs followed by consolidation using SPS, and also discusses their various mechanical properties. Additionally, we present a brief idea about research publications in HEA, and the top 10 countries that have published research articles on HEAs. From 2010 to 18 April 2022, more than 7700 Scopus-indexed research articles on all the fields of HEA and 130 research articles on HEA prepared by mechanical alloying alone have been published.

Alloys doi: 10.3390/alloys1010007

Authors: Theerawat Kumnorkaew Junhe Lian Vitoon Uthaisangsuk Wolfgang Bleck

Carbide-free bainitic steels show attractive mechanical properties but are difficult to process because of the sluggish phase transformation kinetics. A macroscopic model based on the classical nucleation theory in conjunction with the modified Koistinen–Marburger relationship is proposed in this study to simulate the kinetics of incomplete bainitic and martensitic phase transformations with and without austenite deformation. A 0.26C-1Si-1.5Mn-1Cr-1Ni-0.003B-0.03Ti steel and a 0.18C-1Si-2.5Mn-0.2Cr-0.2Ni-0.02B-0.03Ti steel were investigated with different levels of ausforming. The concept of ausforming is expected to accelerate the onset of the bainitic transformation and to enhance the thermodynamic stability of austenite by increased dislocation density. The phase transformation kinetics of both steels is quantitatively analyzed in the study by dilatometry and X-ray diffraction so that the carbon concentration in the retained austenite and bainitic ferrite, as well as their volume fractions, is determined. A critical comparison of the numerical and experimental data demonstrates that the isothermal kinetics of bainite formation and the variation of driving energy can be satisfactorily described by the developed model. This model captures the incompleteness of the bainite phase transformation and the carbon enrichment in the austenite well. A fitting parameter can be used to elucidate the initial energy barrier caused by the ausforming. An increase in austenite stability can be described by the nucleation reaction and the thermodynamic energies associated with the change of dislocation density. The proposed model provides an in-depth understanding of the effect of ausforming on the transformation kinetics under different low-carbon steels and is a potential tool for the future design of heat treatment processes and alloys.

Alloys doi: 10.3390/alloys1010006

Authors: Alexandros E. Karantzalis Anthoula Poulia Spyros Kamnis Athanasios Sfikas Anastasios Fotsis Emmanuel Georgatis

The classic Cantor (FeCoCrMnNi) isoatomic high entropy alloy was modified by separate additions of Mo and Nb in an effort to optimize its mechanical properties and sliding wear response. It was found that the introduction of Mo and Nb modified the single phase FCC solid solution structure of the original alloy and led to the formation of new phases such as the BCC solid solution, σ-phase, and Laves, along with the possible existence of intermetallic phases. The overall phase formation sequence was approached by parametric model assessment and solidification considerations. Nanoindentation-based mechanical property evaluation showed that due to the introduction of Mo and Nb; the modulus of elasticity and microhardness were increased. Creep nanoindentation assessment revealed the beneficial action of Mo and Nb in increasing the creep resistance based on the stress sensitivity exponent, strain rate sensitivity, and critical volume for the dislocation nucleation considerations. The power law and power law breakdown were identified as the main creep deformation mechanisms. Finally, the sliding wear response was increased by the addition of Mo and Nb with this behavior obeying Archard’s law. A correlation between microstructure, wear track morphologies, and debris characteristics was also attempted.

Alloys doi: 10.3390/alloys1010005

Authors: Joseph Robson Jiaxuan Guo Alec Davis

Magnesium–Aluminium alloys can decompose from a supersaturated solid solution by either continuous or discontinuous precipitation. Deformation prior to precipitation has been shown to strongly suppress the discontinuous precipitation mode and promote continuous precipitation. In this work, a model is used to explore the interaction between deformation and precipitation in the Mg–Al system. It has been shown that accelerated nucleation of continuous precipitates on dislocations is predicted to have the dominant effect in suppressing discontinuous precipitation by reducing the solute supersaturation. A secondary effect is the direct role played by twins in the deformed structure, which act as impenetrable barriers to discontinuous precipitate growth. However, even in the deformed case, small regions of discontinuous precipitation are still observed. It is proposed that this is due to the high level of strain concentration expected in the grain boundary regions, which provides a locally enhanced driving force for the migration of grain boundaries such that limited discontinuous precipitation occurs before continuous precipitation becomes established.

Alloys doi: 10.3390/alloys1010004

Authors: Christof J. J. Torrent Philipp Krooß Jingyuan Huang Markus Voigt Christoph Ebbert Steffen Knust Guido Grundmeier Thomas Niendorf

Additive manufacturing (AM) processes are not solely used where maximum design freedom meets low lot sizes. Direct microstructure design and topology optimization can be realized concomitantly during processing by adjusting the geometry, the material composition, and the solidification behavior of the material considered. However, when complex specific requirements have to be met, a targeted part design is highly challenging. In the field of biodegradable implant surgery, a cytocompatible material of an application-adapted shape has to be characterized by a specific degradation behavior and reliably predictable mechanical properties. For instance, small amounts of oxides can have a significant effect on microstructural development, thus likewise affecting the strength and corrosion behavior of the processed material. In the present study, biocompatible pure Fe was processed using electron powder bed fusion (E-PBF). Two different modifications of the Fe were processed by incorporating Fe oxide and Ce oxide in different proportions in order to assess their impact on the microstructural evolution, the mechanical response and the corrosion behavior. The quasistatic mechanical and chemical properties were analyzed and correlated with the final microstructural appearance.

Alloys doi: 10.3390/alloys1010003

Authors: Reza Mahjoub Nikki Stanford

First principles calculations were carried out on six different grain boundaries with complex, non-symmetrical, crystallography’s. Solute species (Gd and Zn) were placed in multiple locations to investigate their effect on the boundary energetics. The grain boundaries were found to have an intrinsic grain boundary energy, and this energy was not markedly affected by the solute concentration at the boundary. However, the work of separation (WSEP) was very sensitive to grain boundary chemistry. Boundaries of higher disorder were found to be more sensitive to boundary chemistry and showed higher values of WSEP and in the case of Gd, were more sensitive to solute concentration at the boundary. No correlation between the boundary behaviour and crystallography could be found, apart from the over-riding conclusion that all six boundaries showed markedly different behaviours, and the effect of solute on each were unique.

Alloys doi: 10.3390/alloys1010002

Authors: Mario Wolf Jan Flormann Timon Steinhoff Gregory Gerstein Florian Nürnberger Hans Jürgen Maier Armin Feldhoff

A new approach for the development of thermoelectric materials, which focuses on a high-power factor instead of a large figure of merit zT, has drawn attention in recent years. In this context, the thermoelectric properties of Cu-Ni-based alloys with a very high electrical conductivity, a moderate Seebeck coefficient, and therefore a high power factor are presented as promising low-cost alternative materials for applications aiming to have a high electrical power output. The Cu-Ni-based alloys are prepared via an arc melting process of metallic nanopowders. The heavy elements tin and tungsten are chosen for alloying to further improve the power factor while simultaneously reducing the high thermal conductivity of the resulting metal alloy, which also has a positive effect on the zT value. Overall, the samples prepared with low amounts of Sn and W show an increase in the power factor and figure of merit zT compared to the pure Cu-Ni alloy. These results demonstrate the potential of these often overlooked metal alloys and the utilization of nanopowders for thermoelectric energy conversion.

Alloys doi: 10.3390/alloys1010001

Authors: Nikki Stanford

Humans have made alloys for thousands of years [...]