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A special issue of Crystals (ISSN 2073-4352). This special issue belongs to the section "Crystalline Metals and Alloys".

Deadline for manuscript submissions: 20 June 2025 | Viewed by 9336

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Dr. Marianthi Bouzouni

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1. Department of Physical Metallurgy and Forming, Hellenic Research Centre for Metals S.A.—ELKEME S.A, 61st km Athens-Lamia Nat. Road, 32011 Oinofyta, Greece
2. Laboratory of Physical Metallurgy, Division of Metallurgy and Materials, School of Mining & Metallurgical Engineering, National Technical University of Athens, 9, Her. Polytechniou Str, Zografos, 15780 Athens, Greece
Interests: physical metallurgy; modeling and simulation; microstructures; characterization; alloy design

Prof. Dr. Shouxun Ji

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Brunel Centre for Advanced Solidification Technology (BCAST), Brunel University London, Uxbridge UB8 3PH, UK
Interests: solidification of metallic alloys; aluminum alloys; magnesium alloys; phase transformation; microstructure and mechanical properties; dissimilar metals and alloys: microstructure and mechanical properties; laser welding
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Special Issue Information

Dear Colleagues,

The core of physical metallurgy is the processing–microstructure–properties relationship in metals and alloys. Optimum mechanical properties are achieved by obtaining a desired microstructure, which is the result of the development and control of processing routes, as well as careful chemical composition selection. The ever-increasing demand for alloys with mechanical properties fit for purpose that fulfill requirements such as a lightweight design, complex geometry, and endurance in extreme environmental conditions has led to the development of sophisticated processing methods and the incorporation of high-resolution characterization techniques regarding microstructural constituents, even in industrial practices. Moreover, the computational modeling and simulation of processes and microstructures at multi-scale levels is a cost-effective solution, providing insights into how various parameters influence the microstructure–properties relationships in alloy design. Within this context, this Special Issue of Crystals will cover the “Advances in Processing, Simulation and Characterization of Alloys”. The aim of this Special Issue is to bring together experts from academia and industry in order to encapsulate the current state of the art in the fields of processing, modeling, and simulation approaches in manufacturing processes and microstructural evolution, as well as characterization techniques, in order to gain a deeper understanding of properties–microstructure relationships. We welcome submissions in the form of both research articles containing original experimental and/or computational results or review articles.

Dr. Marianthi Bouzouni
Prof. Dr. Shouxun Ji
Guest Editors

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Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

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Keywords

process optimization
mechanical properties
microstructures
microstructural characterization
alloy design
modeling and simulation
heat treatments
finite element analysis (FEA)
phase transformations

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Published Papers (10 papers)

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Research

26 pages, 12252 KiB

Open AccessArticle

Phase-Field Simulation of the Creep Mechanism in the AZ31 Magnesium Alloy Under Discontinuous Dynamic Recrystallization Dominance

by Alireza Rezvani, Ramin Ebrahimi and Ebad Bagherpour

Crystals 2025, 15(5), 453; https://doi.org/10.3390/cryst15050453 - 12 May 2025

Viewed by 267

Abstract

Discontinuous dynamic recrystallization is a critical microstructural evolution mechanism during high-temperature deformation, influencing material properties significantly. This study develops a two-dimensional phase-field model to predict steady-state creep rates in the AZ31 magnesium alloy, focusing on DRX during creep. To enhance simulation accuracy, initial microstructures are generated from optical microscopy data, enabling simulations at larger scales with higher representativeness. A novel nucleation methodology is implemented, eliminating the need for nuclei order parameter adaptation, improving computational efficiency. Finite element analysis (FEA) is integrated to capture initial instantaneous deformation. The Kocks–Mecking model is employed to describe the evolution of average dislocation density, accounting for work hardening and dynamic recovery within the initial polycrystalline microstructure. Instead of conventional creep testing, impression creep, a cost-effective alternative, is used for validation. This method provides constant stress and steady penetration velocity, simulating creep conditions effectively. The model accurately predicts recrystallization kinetics and microstructural evolution, exhibiting a strong correlation with experimental results, with an error of approximately 5%. This research provides a robust and efficient approach for predicting creep behavior in high-temperature applications, vital for optimizing material selection and predicting component lifespan in industries. The methodology offers a significant advancement in understanding and predicting DRX-driven creep behavior. Full article

(This article belongs to the Special Issue Advances in Processing, Simulation and Characterization of Alloys)

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14 pages, 4115 KiB

Open AccessArticle

Process Optimization Simulation of Residual Stress in Martensitic Steel Considering Phase Transformation

by Yuzheng Cui and Guang Yang

Crystals 2025, 15(4), 330; https://doi.org/10.3390/cryst15040330 - 30 Mar 2025

Viewed by 283

Abstract

The solid phase transformation of martensitic steel during heat treatment will affect the stress and temperature. Previous residual stress prediction models ignore the effect of phase transition on residual stress. In order to predict residual stress accurately, a residual stress calculation method considering solid phase transition was presented. The measures to reduce residual stress in quenching medium, cooling rate, and the starting temperature and tempering temperature of the martensitic transformation were studied. The experimental results show that residual stress decreases after air cooling. In a certain range, residual stress can be reduced during heat treatment by decreasing the cooling rate and the martensite start temperature. The recommended tempering temperature is 380 °C. Full article

(This article belongs to the Special Issue Advances in Processing, Simulation and Characterization of Alloys)

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21 pages, 24787 KiB

Open AccessArticle

Constitutive Equation and Heat Distortion Behavior of TA4 Titanium Alloy

by Lifeng Ma, Wenshuai Liu, Yanchun Zhu, Ling Qin and Jingfeng Zou

Crystals 2025, 15(4), 290; https://doi.org/10.3390/cryst15040290 - 22 Mar 2025

Viewed by 292

Abstract

In this study, the high-temperature thermal deformation behavior of the TA4 alloy was investigated by thermal compression experiments. The effects of deformation temperature and strain rate on the rheological stress are described by analyzing the variation of stress–strain curves with different parameters and establishing the constitutive equation based on the dynamic material theory model. Thermal processing diagrams were established and plotted to analyze the optimal processing zone and the destabilization zone under different strains. From the thermal machining diagram, it can be concluded that the optimum machining zone at a strain of 0.9 is 1040~1133 K/0.01~0.7 s⁻¹. The optimum machining zone at a strain of 0.6 is 940~1000 K/0.01~0.04 s⁻¹. The optimum machining zone at a strain of 0.3 is 940~1000 K/0.01~0.08 s⁻¹. The effects of different deformation conditions on the thermal deformation mechanism were analyzed in conjunction with EBSD characterization. The results showed that dynamic recrystallization (DRX) was the main deformation softening mechanism when at low strain rate (≤0.1 s⁻¹). At higher strain rates (>0.1 s⁻¹) and lower temperatures (<1083 K and ≥933 K), the main deformation softening mechanism was DRV; at higher temperatures (≥1083 K and ≤1133 K), the main deformation softening mechanism was DRX. Full article

(This article belongs to the Special Issue Advances in Processing, Simulation and Characterization of Alloys)

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20 pages, 552 KiB

Open AccessArticle

On Modeling X-Ray Diffraction Intensity Using Heavy-Tailed Probability Distributions: A Comparative Study

by Farouq Mohammad A. Alam

Crystals 2025, 15(2), 188; https://doi.org/10.3390/cryst15020188 - 16 Feb 2025

Viewed by 550

Abstract

Crystallography, a cornerstone of materials science, provides critical insights into material structures through techniques such as X-ray diffraction (XRD). Among the metrics derived from XRD, intensity serves as a key parameter, reflecting the electron density distribution and offering information about atomic arrangements and sample quality. Due to its inherent variability and susceptibility to extreme values, intensity is best modeled using heavy-tailed, location-scale probability distributions. This paper investigates the model parameter estimation problem for three such distributions—log-Cauchy, half-Cauchy, and Cauchy Birnbaum–Saunders—using several methods, including maximum likelihood and the maximum product of spacings estimation methods. Monte Carlo simulations are conducted to assess the performance of these methods across various scenarios. Additionally, two real XRD intensity datasets are analyzed to compare the applicability and effectiveness of the proposed models. The results demonstrate the potential of heavy-tailed distributions for modeling XRD intensity data, providing a robust framework for future research and practical applications in material characterization. Full article

(This article belongs to the Special Issue Advances in Processing, Simulation and Characterization of Alloys)

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14 pages, 7852 KiB

Open AccessArticle

Effects of Y Additions on the Microstructure and Mechanical Properties of CoCr_1.7Ni Medium-Entropy Alloys

by Shaoshuai Zhou, Xiaoyong Shu, Linli Hu, Xunyu Yuan, Panpan Qiu and Xiwen Xu

Crystals 2025, 15(2), 172; https://doi.org/10.3390/cryst15020172 - 10 Feb 2025

Viewed by 551

Abstract

In order to improve the room temperature yield strength of X and enhance its engineering applicability, a series of CoCr_1.7NiY_x (x = 0, 0.01, 0.02, 0.03, 0.04, and 0.1 at.%) medium-entropy alloys were synthesized to investigate the effect of Y addition on the microstructures and mechanical properties of the CoCr_1.7Ni-based alloy. The X-ray diffraction results show that the alloys exhibit face-centered cubic (FCC) + body-centered cubic (BCC) + hexagonal close packing (HCP) triphasic structure when the Y is adopted, whereas the CoCr_1.7Ni-based alloy has a FCC+BCC biphasic structure. The volume fraction of BCC and HCP phase increased with increasing Y content, which led to alloy grain refinement. As a result, the microhardness and strength of alloys were both enhanced. The addition of Y resulted in dispersion strengthening and solid solution strengthening of CoCr_1.7Ni alloy, the appearance of HCP, and an increase in BCC, which improved the room temperature yield strength and hardness of CoCr_1.7Ni alloy. In particular, for CoCr_1.7NiY_0.1 alloy, its microhardness and yield strength, respectively, increased by 98.18% and 260.59% as compared with those of CoCr_1.7Ni alloy. Full article

(This article belongs to the Special Issue Advances in Processing, Simulation and Characterization of Alloys)

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16 pages, 35462 KiB

Open AccessArticle

Research on the Microstructure and Properties of Arc-Sprayed Austenitic Stainless Steel and Nickel-Based Alloy Composite Coatings with Different Spraying Distances

by Jingang Yan, Zhenming Yang, Limin Zhang and Jianxin Wang

Crystals 2025, 15(2), 142; https://doi.org/10.3390/cryst15020142 - 28 Jan 2025

Cited by 1 | Viewed by 527

Abstract

1Cr18Ni9Ti and Monel composite metal coatings with five different spraying distances were prepared by arc spraying technology. The density, hardness, friction, and wear properties and acid corrosion rate of the coatings with different spraying distances were studied by X-ray diffraction, scanning electron microscopy, Rockwell hardness test, and friction and wear test. Research shows that the spraying distance has a significant effect on the density, hardness, porosity, friction, and wear properties and corrosion rate of the coating. When the spraying distance is 250 mm, the coating has the maximum density and hardness, the minimum porosity and corrosion rate, and the minimum friction coefficient and wear volume. Cu3.8ni and cr0.19fe0.7ni0.11 compounds in the coating have significant effects on the friction, wear, and hardness of the coating. The results show that too-high or too-low spraying distance will lead to pores and large particle agglomeration in the coating, which will affect the surface physical properties of the coating. Full article

(This article belongs to the Special Issue Advances in Processing, Simulation and Characterization of Alloys)

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26 pages, 16648 KiB

Open AccessArticle

Compositional Design, Microstructure, and Thermal Processing of Aluminum-Based Complex Concentrated Alloys

by Spyridon Chaskis, Constantinos Tiktopoulos, Evangelos Gavalas, Marianthi Bouzouni, Fotis Tsiolis and Spyros Papaefthymiou

Crystals 2025, 15(1), 88; https://doi.org/10.3390/cryst15010088 - 17 Jan 2025

Viewed by 952

Abstract

Three lightweight aluminum-based complex concentrated alloys with chemical compositions that have not been previously studied were manufactured and studied: Al₅₂Mg_9.6Zn₁₆Cu_15.5Si_6.9 w.t.% or Al₆₃Mg₁₃Zn₈Cu₈Si₈ a.t.% (alloy A), Al₄₄Mg₁₈Zn₁₉Cu₁₉ w.t.% or Al₅₅Mg₂₅Zn₁₀Cu₁₀ a.t.% (alloy B), and Al₄₇Mg_21.4Zn₁₂Cu_9.7Si_9.7 w.t.% or Al_52.7Mg_26.6Zn_5.6Cu_4.6Si_10.4 a.t.% (alloy AM), with low densities of 3.15 g/cm³, 3.18 g/cm³ and 2.73 g/cm³, respectively. During alloy design, the CALPHAD method was used to calculate a variety of phase diagrams for the various chemical compositions and to predict possible phases that may form in the alloy. The CALPHAD methodology results showed good agreement with the experimental results. The potential of the designed alloys to be used in some industrial applications was examined by manufacturing them using standard industrial techniques, something that is a rarity in this field. The alloys were produced using an induction furnace and pour mold casting process, while industrial-grade raw materials were utilized. Heat treatments with different soaking times were performed in order to evaluate the possibility of improving the mechanical properties of the alloys. Alloys A and AM were characterized by a multiphase microstructure with a dendritic FCC-Al matrix phase and various secondary phases (Q-AlCuMgSi, Al₂Cu and Mg₂Si), while alloy B consisted of a parent phase T-Mg₃₂(Al,Zn)₄₉ and the secondary phases α-Al and Mg₂Si. The microstructure of the cast alloys did not appear to be affected by the heat treatments compared to the corresponding as-cast specimens. However, alterations were observed in terms of the elemental composition of the phases in alloy A. In order to investigate and evaluate the mechanical properties of the as-cast and heat-treated alloys, hardness testing along with electrical conductivity measurements were conducted at room temperature. Among the as-cast samples, alloy AM had the highest hardness (246 HV₄), while among the heat-treated ones, alloy A showed the highest value (256 HV₄). The electrical conductivity of all the alloys increased after the heat treatment, with the highest increase occurring during the first 4 h of the heat treatment. Full article

(This article belongs to the Special Issue Advances in Processing, Simulation and Characterization of Alloys)

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19 pages, 3747 KiB

Open AccessEditor’s ChoiceArticle

Ductility Index for Refractory High Entropy Alloys

by Ottó K. Temesi, Lajos K. Varga, Nguyen Quang Chinh and Levente Vitos

Crystals 2024, 14(10), 838; https://doi.org/10.3390/cryst14100838 - 27 Sep 2024

Cited by 1 | Viewed by 1380

Abstract

The big advantage of refractory high entropy alloys (RHEAs) is their strength at high temperatures, but their big disadvantage is their brittleness at room temperature, which prevents their machining. There is a great need to classify the alloys in terms of brittle-ductile (B-D) properties, with easily obtainable ductility indices (DIs) ready to help design these refractory alloys. Usually, the DIs are checked by representing them as a function of fraction strain, ε. The critical values of DI and ε divide the DI—ε area into four squares. In the case of a successful DI, the points representing the alloys are located in the two diagonal opposite squares, well separating the alloys with (B-D) properties. However, due to the scatter of the data, the B-D separation is not perfect, and it is difficult to establish the critical value of DI. In this paper, we solve this problem by replacing the fracture strain parameter with new DIs that scale with the old DIs. These new DIs are based on the force constant and amplitude of thermal vibration around the Debye temperature. All of them are easily available and can be calculated from tabulated data. Full article

(This article belongs to the Special Issue Advances in Processing, Simulation and Characterization of Alloys)

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18 pages, 2934 KiB

Open AccessArticle

Molecular Dynamics Analysis of Collison Cascade in Graphite: Insights from Multiple Irradiation Scenarios at Low Temperature

by Marzoqa M. Alnairi and Mosab Jaser Banisalman

Crystals 2024, 14(6), 522; https://doi.org/10.3390/cryst14060522 - 30 May 2024

Viewed by 1150

Abstract

In our study, we utilize molecular dynamics simulations, specifically through the Reactive Empirical Bond Order, to unravel atomic-scale dynamics in graphite, an essential component in many advanced technologies, under varying irradiation scenarios. We shed light on the behavior of graphite when exposed to Primary Knock-on Atom (PKA) energies of 10, 20, 40, and 80 keV. The findings highlight the radiation vulnerability of graphite, especially when influenced by hydride inclusion. Both pristine graphite and its hydride variant exhibited an increase in Frenkel pairs (FPs) with escalating PKA energies. Notably, carbon PKAs manifested significant FP effects, whereas hydrogen PKAs influenced defect formation through variable diffusivity. In tested radiation scenarios, particularly in Mode C and the R1 region, cascade patterns identified distinct defect forms of diamond-like and elongated-diamond-like shapes, distinct from the typical PKA collision clusters. Furthermore, our cascade findings emphasize the formation of three-coordinated graphite rings, particularly as PKA energies increase. The graphite population statistics reveal a decline in threefold-coordinated atoms and an increase in other types of defects, with 7-carbon atom rings being the most common. Our research highlights the significance of understanding three-coordinated graphite rings, especially as PKA energies rise. Graphite population statistics reveal a decline in threefold-coordinated atoms and a rise in other defects. Notably, 7-carbon atom rings are the most common. From a clustering perspective, self-interstitial atom (SIA) clusters predominated in pristine graphite, while this trend balanced in the hydride variant. Our research highlights the importance of understanding atomic behaviors in graphite under several radiation scenarios. This knowledge is needed for advancing reliable and efficient technological applications, particularly in the field of nuclear technology. Our research underscores the need to understand atomic behaviors in graphite under radiation, paving the way for detailed study on reliable efficient technological applications. Full article

(This article belongs to the Special Issue Advances in Processing, Simulation and Characterization of Alloys)

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21 pages, 24176 KiB

Open AccessArticle

Effect of Ultrasonic Vibration on Tensile Mechanical Properties of Mg-Zn-Y Alloy

by Wenju Yang, Zhichao Xu, Feng Xiong, Haolun Yang, Xuefeng Guo and Hongshan San

Crystals 2024, 14(1), 39; https://doi.org/10.3390/cryst14010039 - 28 Dec 2023

Cited by 3 | Viewed by 1906

Abstract

Ultrasonic vibration assisted (UVA) plastic forming technology has proven to be a highly effective processing method, particularly for materials that are challenging to deform. In this research, UVA tensile tests were carried out on Mg_98.5Zn_0.5Y₁ alloy at different vibration frequencies and amplitudes. The experimental results indicate that, compared with conventional tensile tests, the yield strength and tensile strength of Mg_98.5Zn_0.5Y₁ alloy exhibit a decrease. Furthermore, the application of ultrasonic vibration demonstrates an ability to enhance the material’s elongation and plasticity. In order to further predict the stress-strain relationship in the metal tensile process, a hybrid constitutive model coupling the frequency and amplitude of ultrasonic vibration was developed based on the modified Johnson Cook model. The calculated results of the constitutive equation are in good agreement with the experimental results, indicating that the established constitutive equation can accurately predict the trend of alloy stress change at different amplitudes and frequencies. It establishes a theoretical foundation for scrutinizing the deformation mechanisms of the alloy under ultrasonic vibration. Furthermore, Abaqus finite element analysis software was employed to simulate and analyze the UVA tensile process, elucidating the impact of ultrasonic vibration on stress distribution, strain patterns, and material flow in the tensile behavior of Mg_98.5Zn_0.5Y₁ alloys. Full article

(This article belongs to the Special Issue Advances in Processing, Simulation and Characterization of Alloys)

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