Metals

13 pages, 1708 KB

Open AccessArticle

Surface Enhancement of CoCrMo Bioimplant Alloy via Nanosecond and Femtosecond Laser Processing with Thermal Treatment

by Hsuan-Kai Lin, Po-Wei Chang, Yu-Ming Ding, Yu-Ting Lyu, Yuan-Jen Chang and Wei-Hua Lu

Metals 2025, 15(9), 980; https://doi.org/10.3390/met15090980 (registering DOI) - 1 Sep 2025

With an aging population, the number of joint replacement surgeries is on the rise. One of the most common implant materials is cobalt–chromium–molybdenum (CoCrMo) alloy. Hence, the surface properties of this alloy have attracted increasing attention. In this study, nanosecond and femtosecond laser [...] Read more.

With an aging population, the number of joint replacement surgeries is on the rise. One of the most common implant materials is cobalt–chromium–molybdenum (CoCrMo) alloy. Hence, the surface properties of this alloy have attracted increasing attention. In this study, nanosecond and femtosecond laser processing, followed by annealing, was employed to modify the CoCrMo surface. The effects of the treatment conditions on the surface morphology, structure, composition, hardness, roughness, contact angle, wear properties, and corrosion current were studied. Femtosecond laser processing with an energy density of 1273 mJ/cm², followed by heat treatment at 160 °C for 2 h, produced laser-induced periodic surface structures (LIPSS) without altering the chemical composition of the alloy and rendered the surface superhydrophobic. In contrast, nanosecond laser treatment at higher laser energy densities promoted the formation of an oxide layer, which improved the hardness and corrosion resistance of the substrate. Overall, the CoCrMo samples processed using the femtosecond laser system exhibited superior corrosion and wear resistance, with a protection efficiency of approximately 92%. Full article

(This article belongs to the Special Issue Surface Treatments and Coating of Metallic Materials)

7 pages, 184 KB

Open AccessEditorial

Mechanical Behaviors and Damage Mechanisms of Metallic Materials

by Denis Benasciutti, Luis Reis and Julian Marcell Enzveiler Marques

Metals 2025, 15(9), 979; https://doi.org/10.3390/met15090979 (registering DOI) - 1 Sep 2025

Abstract

Metallic materials continue to be widely used across both traditional and advanced engineering sectors, including civil, marine, automotive, aeronautics, and aerospace, to name just a few [...] Full article

(This article belongs to the Special Issue Mechanical Behaviors and Damage Mechanisms of Metallic Materials)

18 pages, 3056 KB

Open AccessArticle

A Practical 1D Approach for Real-Time Prediction of Argon Flow and Pressure in Continuous Casting of Steel

by Hyunjin Yang, Bong-Min Jin, Hyeonjin Kim, Seungwon Seo and Seunghyun Sim

Metals 2025, 15(9), 978; https://doi.org/10.3390/met15090978 (registering DOI) - 1 Sep 2025

Abstract

The pressure and flow rate of an argon line embedded within a stopper rod serve as useful industrial indicators and control factors for mitigating air aspiration into the Submerged Entry Nozzle (SEN) during the continuous casting of steel. This manuscript investigates several challenges [...] Read more.

The pressure and flow rate of an argon line embedded within a stopper rod serve as useful industrial indicators and control factors for mitigating air aspiration into the Submerged Entry Nozzle (SEN) during the continuous casting of steel. This manuscript investigates several challenges associated with interpreting monitored argon line pressures and gas flow rates, including variations in gas pressure during delivery, actual volumes of gas entering the nozzle, argon leakage, and air aspiration. To address these issues, a new one-dimensional (1D) analytical model of compressible argon flow in the stopper rod was developed, incorporating gas dynamics and heat transfer. This concise 1D model was validated using data from a continuous casting simulator (CCS) employing a low-melting-point Bi-Sn alloy (melting point 137 °C). Pilot trials were conducted to replicate various industrial casting scenarios, generating datasets for model validation and demonstration of real-time operation. The 1D model predictions were compared with those from a CFD-based compressible flow model under CCS operating conditions. Following validation, parametric studies were conducted to explore realistic industrial scenarios (e.g., gas flow rate < 5 SLPM, nozzle diameter < 5 mm), including extreme conditions such as air aspiration and choking: a critical nozzle diameter (1.223 mm) corresponds to choked flow, limiting the maximum achievable gas flow rate to 5 SLPM. Additionally, the real-time prediction capabilities of the model were demonstrated using measured argon line pressures and flow rates from CCS trials. The proposed 1D model thus provides a practical tool for accurately interpreting SEN flow conditions from monitored argon pressures and effectively estimating argon bubble injection by clarifying actual gas pressures and flow rates at the stopper injection point. Full article

(This article belongs to the Special Issue Advanced Metal Casting Processes: Latest Research, Insights, and Challenges)

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17 pages, 3046 KB

Open AccessArticle

A New Approach in Hydrometallurgy for the Solvent Extraction of Cu(II) from Alkaline Solutions Leached with Tartrate Using Phenyl-2-Pyridyl Ketoxime

by Félix José Sueros Velarde, Jhon Alfredo Quispe Ortiz and Angela F. Danil de Namor

Metals 2025, 15(9), 977; https://doi.org/10.3390/met15090977 (registering DOI) - 31 Aug 2025

Abstract

For the first time, an alternative and sustainable approach is reported using phenyl-2-pyridyl ketoxime (PPKO) as a selective extracting agent for the recovery of Cu(II) from alkaline solutions in the presence of tartrate ions. The advantages relative to conventional processes carried out in [...] Read more.

For the first time, an alternative and sustainable approach is reported using phenyl-2-pyridyl ketoxime (PPKO) as a selective extracting agent for the recovery of Cu(II) from alkaline solutions in the presence of tartrate ions. The advantages relative to conventional processes carried out in acidic media are outlined. Through potentiometric and spectrophotometric analyses, the sequential formation of a 1:2 metal cation–ligand Cu(II)-(PPKO)₂ complex was identified as the predominant species in alkaline aqueous solutions. The high removal capacity of the extractant for Cu(II), as assessed from liquid–liquid extraction, and its efficient performance are comparable to widely used commercial extractants. Thermodynamic studies of the complexation between the copper(II) ion and PPKO demonstrated that the process exhibits an endothermic character. A progressive decrease in the performance of the extractant was observed after reuse without a regenerative treatment. This deterioration was partially reversed through a controlled reprotonation process using an acetate buffer solution. Overall, the results support the potential of PPKO as an effective and selective alternative ligand for hydrometallurgical applications in alkaline medium. Full article

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4 pages, 154 KB

Open AccessEditorial

Metal Crystal and Polycrystal Plastic Strain Hardening

by John D. Clayton

Metals 2025, 15(9), 976; https://doi.org/10.3390/met15090976 (registering DOI) - 31 Aug 2025

Abstract

Crystalline metallic solids are key components of engineering devices and structures whose manufacture and performance often crucially involve, or seek to minimize, plastic deformation phenomena [...] Full article

(This article belongs to the Special Issue Editorial Board Members’ Collection Series: Metal Crystal/Polycrystal Plastic Strain Hardening)

17 pages, 4031 KB

Open AccessArticle

Experimental Study on Fatigue Performance of Q355D Notched Steel Under High-Low Frequency Superimposed Loading

by Xianglong Zheng, Jiangyi Zhou and He Zhang

Metals 2025, 15(9), 975; https://doi.org/10.3390/met15090975 (registering DOI) - 31 Aug 2025

Abstract

During the service life of steel bridges, the structural stress histories display combined cyclic characteristics due to the superposition of low-frequency thermal loading and high-frequency vehicle loading. To investigate the fatigue performance under such loading patterns, a series of constant-amplitude and high-low frequency [...] Read more.

During the service life of steel bridges, the structural stress histories display combined cyclic characteristics due to the superposition of low-frequency thermal loading and high-frequency vehicle loading. To investigate the fatigue performance under such loading patterns, a series of constant-amplitude and high-low frequency superimposed loading fatigue (HLSF) tests were conducted on notched specimens fabricated from Q355D bridge steel. The influence of HLSF waveform parameters on fatigue life was systematically investigated. Based on the fracture evolution mechanism, a concept of low-frequency periodic damage acceleration factor was proposed to effectively model the block nonlinear damage effects, and the applicability of existing fatigue life prediction models was discussed. The results show that the effect of average stress on the fatigue life under HLSF can be effectively considered by Walker’s formula. Low-amplitude ratios and low-frequency ratios indicate unfavorable loading conditions that may accelerate the Q355D fatigue damage accumulation, and these conditions are not adequately accounted for in current life prediction models. Compared to constant amplitude loading, HLSF can lead to a 66% and 46% reduction in high-frequency life when the amplitude ratio reaches 0.12 and the frequency ratio reaches 100. Compared to Miner’s rule, the proposed damage correction method reduces the life prediction error for HLSF by 11%. These findings provide valuable references for the fatigue assessment of bridge steel structures under the coupled effects of temperature and vehicle loading. Full article

(This article belongs to the Special Issue Fatigue and Damage in Metallic Materials)

15 pages, 14986 KB

Open AccessArticle

The Effect of Annealing and Aging Temperature on the Microstructure and Properties of an 800 MPa Grade Dual-Phase Steel with High Formability

by Mengling Li, Yuebiao Yang, Yongxu Gao, Xiufei Zhang, Bin Lu and Zhengzhi Zhao

Metals 2025, 15(9), 974; https://doi.org/10.3390/met15090974 (registering DOI) - 30 Aug 2025

Abstract

To develop automotive steel with a higher strength–ductility balance, an 800 MPa grade Nb-Ti microalloyed dual-phase steel with high elongation was designed. Continuous annealing tests were conducted using a continuous annealing simulation testing machine. The effects of annealing temperature and aging temperature on [...] Read more.

To develop automotive steel with a higher strength–ductility balance, an 800 MPa grade Nb-Ti microalloyed dual-phase steel with high elongation was designed. Continuous annealing tests were conducted using a continuous annealing simulation testing machine. The effects of annealing temperature and aging temperature on the microstructure and mechanical properties were investigated through SEM, EBSD, TEM, and tensile testing. The results indicate that the microstructure of the steel primarily consists of ferrite, martensite, and a small amount of retained austenite. As the annealing temperature rises, the martensite content increases, and the retained austenite content first increases and then decreases. Therefore, the tensile strength and elongation initially increase and then decrease, while the yield strength gradually decreases. As the aging temperature rises, the martensite content decreases, while the tempering degree of martensite increases and the retained austenite content rises. Therefore, the tensile strength gradually decreases, and the yield strength and elongation gradually increase. The optimal comprehensive performance was achieved with an annealing temperature of 830 °C and an aging temperature of 330 °C, resulting in a tensile strength of 915 MPa, a yield strength of 470 MPa, and an elongation of 24.4%. This represents a 28.4% increase in elongation compared to conventional dual-phase steels of the same strength grade. The strength–ductility product reaches 22.3 GPa%. Full article

(This article belongs to the Special Issue Advanced High-Performance Steels: From Fundamental to Applications)

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19 pages, 6857 KB

Open AccessArticle

Reduction Behavior of Biochar-in-Plant Fines Briquettes for CO₂-Reduced Ironmaking

by Hesham Ahmed, Mohamed Elsadek, Maria Lundgren and Lena Sudqvist Öqvist

Metals 2025, 15(9), 973; https://doi.org/10.3390/met15090973 (registering DOI) - 30 Aug 2025

Abstract

Blast furnace (BF) ironmaking remains one of the most efficient countercurrent processes; however, achieving further CO₂ emission reductions through conventional methods is increasingly challenging. Currently, BF ironmaking emits approximately 2.33 tonnes of fossil-derived CO₂ per tonne of crude steel cast. Integrating [...] Read more.

Blast furnace (BF) ironmaking remains one of the most efficient countercurrent processes; however, achieving further CO₂ emission reductions through conventional methods is increasingly challenging. Currently, BF ironmaking emits approximately 2.33 tonnes of fossil-derived CO₂ per tonne of crude steel cast. Integrating briquettes composed of biochar and in-plant fines into the BF process offers a promising short- to medium-term strategy for lowering emissions. This approach enables efficient recycling of fine residues and the substitution of fossil reductants with bio-based alternatives, thereby improving productivity while reducing energy and carbon intensity. This study investigates the reduction behavior of (i) biochar mixed with pellet fines, (ii) various in-plant residues individually, and (iii) briquettes composed of biochar and in-plant fines. The reduction rate of biochar–pellet fine mixtures was found to depend on biochar type, with pyrolyzed pine sawdust exhibiting the highest reactivity, and pyrolyzed contorta wood chips the lowest. A correlation between reduction rate and the alkali index of each char was established, although other factors such as char origin and physical properties also influenced reactivity. The effect of biochar addition (0, 5, and 10 wt.%) on the reduction of steelmaking residues was also studied. In general, biochar enhanced the reduction degree and shifted the reaction onset to lower temperatures. The produced briquettes maintained high mechanical integrity during and after reduction, regardless of biochar origin. Thermogravimetric and XRD analyses revealed that mass loss initiates with the dehydroxylation of cement phases and release of volatiles, followed by carbonate decomposition and reduction of higher oxides above 500 °C. At temperatures ≥ 850 °C, the remaining iron oxides were further reduced to metallic iron. Full article

(This article belongs to the Section Extractive Metallurgy)

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15 pages, 5574 KB

Open AccessArticle

Development of a TaN-Ce Machine Learning Potential and Its Application to Solid–Liquid Interface Simulations

by Yunhan Zhang, Jianfeng Cai, Hongjian Chen, Xuming Lv and Bowen Huang

Metals 2025, 15(9), 972; https://doi.org/10.3390/met15090972 (registering DOI) - 30 Aug 2025

Abstract

This study develops a machine learning potential (MLP) based on the Moment Tensor Potential (MTP) method for the TaN-Ce system. This potential is employed to investigate the interfacial structure and wetting behavior between liquid Ce and solid TaN. Molecular dynamics (MDs) simulations reveal [...] Read more.

This study develops a machine learning potential (MLP) based on the Moment Tensor Potential (MTP) method for the TaN-Ce system. This potential is employed to investigate the interfacial structure and wetting behavior between liquid Ce and solid TaN. Molecular dynamics (MDs) simulations reveal that liquid Ce exhibits significant wetting on the TaN surface at high temperatures. The interfacial region undergoes pre-melting and component interdiffusion, forming an amorphous transition layer. Nitrogen atoms display high diffusivity, leading to surface mass loss, while tantalum atoms demonstrate excellent thermal stability and penetration resistance. These findings provide theoretical support for the design of interfacial materials and corrosion control in high-temperature metallurgy. Full article

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16 pages, 5620 KB

Open AccessArticle

Influence of Build Orientation and Heat Treatment on the Microstructure and Mechanical Properties of SUS316L Fabricated by Selective Laser Melting

by Yujin Lim, Chami Jeon, Yoon-Seok Lee and Ilguk Jo

Metals 2025, 15(9), 971; https://doi.org/10.3390/met15090971 (registering DOI) - 30 Aug 2025

Abstract

Additive manufacturing (AM) via selective laser melting (SLM) is increasingly deployed in aerospace, biomedical, and tooling applications where complex geometries and high performance are required. Yet, process-induced anisotropy and microstructural heterogeneity can strongly affect mechanical and tribological behavior. This study systematically evaluates the [...] Read more.

Additive manufacturing (AM) via selective laser melting (SLM) is increasingly deployed in aerospace, biomedical, and tooling applications where complex geometries and high performance are required. Yet, process-induced anisotropy and microstructural heterogeneity can strongly affect mechanical and tribological behavior. This study systematically evaluates the combined effects of build orientation (0°, 45°, and 90° relative to the build plate) and post-build heat treatment (as-built, 600 °C, and 860 °C) on the phase constitution, microstructure, hardness, tensile response, and dry sliding wear of SLM-fabricated 316L stainless steel. X-ray diffraction indicated a fully austenitic (γ-fcc) structure without detectable secondary phases across all conditions. Orientation-dependent substructures were observed: ~1 µm equiaxed cellular features at 0°, finer 0.3–0.5 µm cells at 45°, and 1–2 µm elongated features at 90°. Microhardness varied with orientation; relative to 0°, 45° specimens were ~15 HV higher, whereas 90° specimens were ~10 HV lower. Heat treatment at 600 °C promoted refinement and recovery of the cellular network, most pronounced in the 45° orientation, while treatment at 860 °C largely erased melt pool boundary contrast, producing a more homogeneous particle-like microstructure. Tensile fractography revealed dimpled rupture in all cases; the 90° orientation showed finer dimples and lower hardness, consistent with a ductile failure mode under reduced constraint. Dry sliding wear tests identified adhesive wear, intensified by the build-up of transferred fragments, as the dominant mechanism in both as-built and 600 °C conditions. Changes to melt pool morphology after 860 °C heat treatment correlated with altered wear track widths, with the 0° condition showing a notable narrowing relative to the 600 °C state. These results highlight processing pathways for tailoring anisotropy, strength–ductility balance, and wear resistance in SLM 316L. Full article

(This article belongs to the Special Issue Advances in Laser Processing of Metals and Alloys)

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16 pages, 9854 KB

Open AccessArticle

Microstructure and Mechanical Property Evolution of 34CrNiMo6 Steel via Induction Quenching and Tempering

by Bing Kong, Qian Jia, Guohuan Wang, Dong Tao and Zhong Yang

Metals 2025, 15(9), 970; https://doi.org/10.3390/met15090970 (registering DOI) - 30 Aug 2025

Abstract

The induction quenching–tempering process typically enhances the surface strength and core toughness of alloy steels by utilizing the skin effect. However, the impact of parameters like quenching current and heating time on the microstructure and mechanical property of 34CrNiMo6 steel crankshafts remains unclear. [...] Read more.

The induction quenching–tempering process typically enhances the surface strength and core toughness of alloy steels by utilizing the skin effect. However, the impact of parameters like quenching current and heating time on the microstructure and mechanical property of 34CrNiMo6 steel crankshafts remains unclear. In this work, the microstructure of 34CrNiMo6 steel after induction quenching exhibits three distinct zones: a martensite hardened layer; a transition zone of martensite and tempered sorbite; and a matrix of tempered sorbite. As the induction current (400, 500, and 600 mA) and heating time (3, 5, and 7 s) increase, the hardened layer thickness enhances (up to 3.21 mm). Under the 600 mA and 7 s, the hardened layer reaches peak hardness and residual stress values of 521.48 HV and −330.12 MPa, showing a decreasing trend from surface to core. After tempering at 330 °C for 2 h, the hardened layer mainly consists of tempered martensite, and the surface hardness and residual stress decrease to 417.94 HV and −12.33 MPa. The temperature gradient from quenching balances after tempering, with martensitic phase transformation and stress redistribution reducing hardness and residual stress. Furthermore, the induction quenching–tempering process enhances the toughness of 34CrNiMo6 steel when compared to the untreated specimen, boosting its tensile yield strength, elongation, and tensile strength by 15.3%, 14.9%, and 19.5%, respectively. This work deepens the understanding of induction quenching–tempering process and provides valuable insights for designing alloy steels with excellent mechanical properties. Full article

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15 pages, 4381 KB

Open AccessArticle

Microstructure and Mechanical Properties Change of Al7SiMgxEr (x: 0.03–0.1)

by Murat Colak, Enes Aydin Muhammed, Mustafa Turkmen and Derya Dispinar

Metals 2025, 15(9), 969; https://doi.org/10.3390/met15090969 (registering DOI) - 30 Aug 2025

Abstract

Aluminum and its alloys are widely used in many fields, such as automotive, aerospace, and defense industries, due to their many advantages. Due to such critical applications, the quality demands are also increasing. With the recent development in technologies, studies on casting of [...] Read more.

Aluminum and its alloys are widely used in many fields, such as automotive, aerospace, and defense industries, due to their many advantages. Due to such critical applications, the quality demands are also increasing. With the recent development in technologies, studies on casting of aluminum with different alloying element additions are ongoing rapidly. Various elements are added to the alloy to provide the desired properties. In this study, the effects of 0.03, 0.06, and 0.1 wt% Er addition to A356 aluminum alloy were evaluated simply because in the literature, only 0.1 wt% and above additions were studied. Samples were prepared using permanent molds and subjected to mechanical testing and microstructural characterization. Changes in the microstructure (evaluated via SDAS and SDAL) and mechanical properties of the cast specimens were analyzed. The results showed that Er addition improved tensile strength by up to 30%, increased elongation fourfold, and enhanced toughness by a factor of 4.5. Full article

(This article belongs to the Section Metal Casting, Forming and Heat Treatment)

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18 pages, 5211 KB

Open AccessArticle

Data-Driven Performance-Oriented Rapid Process Optimization for 316 Stainless Steels Prepared by Laser Powder Bed Fusion

by Junyan Zhu, Meiling Jiang, Guoliang Huang and Ke Huang

Metals 2025, 15(9), 968; https://doi.org/10.3390/met15090968 (registering DOI) - 30 Aug 2025

Abstract

In this work, a rapid process optimization framework for laser powder bed fusion (LPBF) based on a high-throughput mechanical testing platform and data analytical methods was proposed and validated. This framework enables the efficient building of a process–properties database and analytical model, as [...] Read more.

In this work, a rapid process optimization framework for laser powder bed fusion (LPBF) based on a high-throughput mechanical testing platform and data analytical methods was proposed and validated. This framework enables the efficient building of a process–properties database and analytical model, as well as the fine-tuning of customized mechanical properties. Unlike previous approaches that focused primarily on density as the main optimization target, this method directly aligns the mechanical properties by systematically varying the LPBF process parameters (e.g., laser power, scanning speed, etc.). Tensile specimens in the high densification range were prepared and tested using a high-throughput mechanical property test platform (HTP). Following this, an analytical model correlating tensile properties and process parameters was developed using response surface methodology (RSM). Based on this model recommendation, a specimen with a densification of 99.46% and a yield strength (YS) of 524.74 MPa was achieved, with only a 3.72% variation compared to the predicted value (526.08 MPa), confirming the model’s reliability. A comprehensive analysis of relative density, phase content and microstructure was conducted, comparing them with a specimen exhibiting lower properties. This study provides an effective method for the rapid evaluation and optimization of LPBF processing parameters for fine-tuning customized mechanical properties. Full article

(This article belongs to the Special Issue Welding and Additive Manufacturing of Metals)

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19 pages, 2648 KB

Open AccessArticle

Systematic Study on the Thermal Performance of Casting Slab Under Varying Environmental Conditions

by Guichang Tian, Baokuan Li, Donglin Mo and Jianxiang Xu

Metals 2025, 15(9), 967; https://doi.org/10.3390/met15090967 (registering DOI) - 29 Aug 2025

Abstract

Accurate prediction of slab temperature during the continuous casting and rolling process is essential for optimizing reheating furnace scheduling and achieving energy savings and emission reductions in steel production. However, because of the dynamic boundary conditions caused by the complex transport processes, obtaining [...] Read more.

Accurate prediction of slab temperature during the continuous casting and rolling process is essential for optimizing reheating furnace scheduling and achieving energy savings and emission reductions in steel production. However, because of the dynamic boundary conditions caused by the complex transport processes, obtaining precise temperature data for slabs remains challenging. These difficulties lead to issues such as low hot charging rates, mixing of hot and cold slabs in reheating furnaces, and excessive heat loss from slabs after cutting. To address these challenges, this study develops a mathematical model to calculate slab temperatures during the continuous casting and rolling process, providing a foundation for production scheduling optimization. The model accounts for the coupled heat transfer effects induced by dynamic slab stacking and the stacking heat transfer effects resulting from slabs with varying cross-sectional dimensions. Validation against experimental data demonstrated the model’s accuracy and reliability. Key findings highlighted that neglecting dynamic stacking effects or simplifying slab dimensions introduces errors. These results enhance slab temperature tracking in complex processes and advance related theoretical understanding. Full article

(This article belongs to the Special Issue Computational Methods in Metallic Materials Manufacturing Processes 2025)

44 pages, 1456 KB

Open AccessReview

A Review of Machine Learning Applications on Direct Energy Deposition Additive Manufacturing—A Trend Study

by Syamak Pazireh, Seyedeh Elnaz Mirazimzadeh and Jill Urbanic

Metals 2025, 15(9), 966; https://doi.org/10.3390/met15090966 (registering DOI) - 29 Aug 2025

Abstract

This review explores the evolution and current state of machine learning (ML) and artificial intelligence (AI) applications in direct energy deposition (DED) and wire arc additive manufacturing (WAAM) processes. A Python-based automated search script was developed to systematically retrieve relevant literature using the [...] Read more.

This review explores the evolution and current state of machine learning (ML) and artificial intelligence (AI) applications in direct energy deposition (DED) and wire arc additive manufacturing (WAAM) processes. A Python-based automated search script was developed to systematically retrieve relevant literature using the Crossref API, yielding around 370 papers published between 2010 and July 2025. The study identifies significant growth in ML-related DED research starting in 2020, with increasing adoption of advanced techniques such as deep learning, fuzzy logic, and hybrid physics-informed models. A year-by-year trend analysis is presented, and a comprehensive categorization of the literature is provided to highlight dominant application areas, including process optimization, real-time monitoring, defect detection, and melt pool prediction. Key challenges, such as limited closed-loop control, lack of generalization across systems, and insufficient modeling of deposition-location effects, are discussed. Finally, future research directions are outlined, emphasizing the need for integrated thermo-mechanical models, uncertainty quantification, and adaptive control strategies. This review serves as a resource for researchers aiming to advance intelligent control and predictive modeling in DED-based additive manufacturing. Full article

(This article belongs to the Special Issue Machine Learning in Metal Additive Manufacturing)

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32 pages, 8490 KB

Open AccessArticle

Physics-Based Machine Learning Framework for Predicting Structure-Property Relationships in DED-Fabricated Low-Alloy Steels

by Atiqur Rahman, Md. Hazrat Ali, Asad Waqar Malik, Muhammad Arif Mahmood and Frank Liou

Metals 2025, 15(9), 965; https://doi.org/10.3390/met15090965 (registering DOI) - 29 Aug 2025

Abstract

The Directed Energy Deposition (DED) process has demonstrated high efficiency in manufacturing steel parts with complex geometries and superior capabilities. Understanding the complex interplays of alloy compositions, cooling rates, grain sizes, thermal histories, and mechanical properties remains a significant challenge during DED processing. [...] Read more.

The Directed Energy Deposition (DED) process has demonstrated high efficiency in manufacturing steel parts with complex geometries and superior capabilities. Understanding the complex interplays of alloy compositions, cooling rates, grain sizes, thermal histories, and mechanical properties remains a significant challenge during DED processing. Interpretable and data-driven modeling has proven effective in tackling this challenge, as machine learning (ML) algorithms continue to advance in capturing complex property structural relationships. However, accurately predicting the prime mechanical properties, including ultimate tensile strength (UTS), yield strength (YS), and hardness value (HV), remains a challenging task due to the complex and non-linear relationships among process parameters, material constituents, grain size, cooling rates, and thermal history. This study introduces an ML model capable of accurately predicting the UTS, YS, and HV of a material dataset comprising 4900 simulation analyses generated using the “JMatPro” software, with input parameters including material compositions, grain size, cooling rates, and temperature, all of which are relevant to DED-processed low-alloy steels. Subsequently, an ML model is developed using the generated dataset. The proposed framework incorporates a physics-based DED-specific feature that leverages “JMatPro” simulations to extract key input parameters such as material composition, grain size, cooling rate, and thermal properties relevant to mechanical behavior. This approach integrates a suite of flexible ML algorithms along with customized evaluation metrics to form a robust foundation to predict mechanical properties. In parallel, explicit data-driven models are constructed using Multivariable Linear Regression (MVLR), Polynomial Regression (PR), Multi-Layer Perceptron Regressor (MLPR), XGBoost, and classification models to provide transparent and analytical insight into the mechanical property predictions of DED-processed low-alloy steels. Full article

(This article belongs to the Special Issue Additive Manufacturing of Metallic Materials: Experiments and Modelling)

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26 pages, 15689 KB

Open AccessArticle

Comprehensive Investigation of Coverage Rates of Shot Peening on the Tribological Properties of 6061-T6 Alloy

by Orçun Canbulat and Fatih Bozkurt

Metals 2025, 15(9), 964; https://doi.org/10.3390/met15090964 (registering DOI) - 29 Aug 2025

Abstract

In the search for lightweight and sustainable engineering approaches, enhancing the surface wear resistance of structural materials, such as 6061-T6 aluminum alloy, has become increasingly important. This study investigates the effect of coverage rates on the tribological properties of shot-peened 6061-T6 alloy, aiming [...] Read more.

In the search for lightweight and sustainable engineering approaches, enhancing the surface wear resistance of structural materials, such as 6061-T6 aluminum alloy, has become increasingly important. This study investigates the effect of coverage rates on the tribological properties of shot-peened 6061-T6 alloy, aiming to improve its usage in industries where weight reduction and durability are important, such as aerospace, automotive, railway, and renewable energy systems. A shot peening process was applied at four different coverage rates of 100%, 200%, 500%, and 1500% for comprehensive evaluation. A series of experimental analyses were conducted, including microhardness tests, ball-on-plate wear tests, residual stress measurements, and surface roughness evaluations. Furthermore, microstructural analysis was performed to investigate subsurface deformation, and scanning electron microscopy (SEM) was carried out to identify the wear mechanisms of the worn surfaces in detail. The results demonstrated a clear trend of gradual improvement in wear resistance with increasing shot peen coverage. The sample treated at a 1500% coverage rate exhibited 1.34 times higher hardness and 19 times higher wear resistance compared to the untreated sample. This study highlights that shot peening is an effective and feasible surface engineering method for enhancing the wear performance of 6061-T6 alloy. The findings offer valuable contributions for the development of lightweight and wear-resistant components considering sustainable material design. Full article

21 pages, 7348 KB

Open AccessArticle

Numerical Simulation of the Solid Particle Entrainment Behavior in Bottom-Blown Ladle

by Cheng Wang, Wentao Lou, Jie Zeng, Zeyu Wang and Jianfeng Xie

Metals 2025, 15(9), 963; https://doi.org/10.3390/met15090963 (registering DOI) - 29 Aug 2025

Abstract

The entrainment behavior of solid particles from the top liquid surface into molten steel exerts a crucial influence on rapid slagging and efficient desulfurization during the refining process. A Euler–Euler mathematical model was established to describe the multiphase flow field and the entrainment [...] Read more.

The entrainment behavior of solid particles from the top liquid surface into molten steel exerts a crucial influence on rapid slagging and efficient desulfurization during the refining process. A Euler–Euler mathematical model was established to describe the multiphase flow field and the entrainment behavior of solid particles in a bottom-blown ladle. This model was validated by comparison with water model experiments. The effects of bottom-blowing tuyere number, gas flow rate, and solid particle size on the flow field and particle entrainment behavior were investigated. It was found that increasing the gas flow rate enhances the participation of particles in the ladle; however, the entrainment effect changes minimally when the gas flow rate exceeds 192 Nm³/h. Increasing the number of tuyeres adversely affects particle entrainment and mixing efficiency, while simultaneously expanding the size of the “open eyes”. The particle size of the refining slag has a significant impact on the entrainment effect: when the particle size exceeds 10 mm, the particles are hardly entrained in the ladle. Reducing the particle size is more conducive to increasing the entrainment amount, but excessively small particles will significantly enlarge the size of the “open eyes”. Full article

(This article belongs to the Special Issue Advanced Simulation and Modeling Technologies of Metallurgical Processes—2nd Edition)

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16 pages, 6260 KB

Open AccessArticle

Corrosion Resistance of an Alternative Thermomechanically Processed Ti-23.6Nb-5.1Mo-6.7Zr Alloy for Biomedical Applications

by Aline Raquel Vieira Nunes, Camila Dias dos Reis Barros, Gabriel Gomes Carvalho, Pedro Turetta de Senna, Sinara Borborema, Jean Dille, José Antonio Ponciano Gomes and Luiz Henrique de Almeida

Metals 2025, 15(9), 962; https://doi.org/10.3390/met15090962 (registering DOI) - 29 Aug 2025

Abstract

Metastable titanium alloys have been developed for biomedical use due to their lower elastic modulus, combined with high strength, good ductility, and excellent corrosion resistance. In this study, the electrochemical corrosion resistance of the alternative Ti-23.6Nb-5.1Mo-6.7Zr alloy was investigated. The alloy was initially [...] Read more.

Metastable titanium alloys have been developed for biomedical use due to their lower elastic modulus, combined with high strength, good ductility, and excellent corrosion resistance. In this study, the electrochemical corrosion resistance of the alternative Ti-23.6Nb-5.1Mo-6.7Zr alloy was investigated. The alloy was initially homogenized at 1000 °C for 24 h and then tested under different processing conditions: 90% cold rolling; 90% cold rolling followed by annealing at 950 °C for 1 h and water quenching; and 90% cold rolling followed by aging at 300 °C, 400 °C, and 500 °C for 4 h each. Electrochemical behavior was assessed using anodic polarization, open circuit potential (OCP), and electrochemical impedance spectroscopy (EIS) tests in a synthetic solution (Ringer’s solution) to simulate body fluid. The obtained results demonstrate the stability of the passive film formed of the conventional and modified alloys, considering long-term use in the human body, regardless of the volumetric fraction and phase distribution across the various processing routes studied as β, α, α″ and ω. The electrochemical parameters, combined with Young’s modulus and hardness of the alternative alloys, enable the definition of a multicriteria selection method of the most suitable mechanical process routes to be used. The application focused on components of functional femoral stems. Full article

(This article belongs to the Special Issue Titanium Alloys: Processing, Properties and Applications)

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