Metals

17 pages, 6339 KiB

Open AccessArticle

Influence of Copper Stoichiometric Composition and Compaction Method on Mechanical Properties of Cu_xSe Thermoelectric Materials

by Fani Stergioudi, Georgios Skordaris, Maria Pappa, Nikolaos Michailidis, Vasileios Pavlidis, Dimitrios Stathokostopoulos, Aikaterini Teknetzi, Lamprini Malletzidou, George Vourlias, Georgios Maliaris and Ioanna K. Sfampa

Metals 2025, 15(6), 640; https://doi.org/10.3390/met15060640 - 6 Jun 2025

Abstract

This study investigates the structural and mechanical properties of Cu–Se-based thermoelectric materials with varying Cu:Se stoichiometries (1.8, 1.9, and 2.0). Phase composition was examined using X-ray diffraction (XRD), revealing a transition from a mixed α/β-phase in Cu:Se = 2.0 to a fully cubic [...] Read more.

This study investigates the structural and mechanical properties of Cu–Se-based thermoelectric materials with varying Cu:Se stoichiometries (1.8, 1.9, and 2.0). Phase composition was examined using X-ray diffraction (XRD), revealing a transition from a mixed α/β-phase in Cu:Se = 2.0 to a fully cubic β-phase Cu_2−xSe in Cu:Se = 1.8. Crystallite size analysis showed a reduction with increasing Cu content, which strongly influenced mechanical behavior. Vickers microhardness and nanoindentation tests were employed to assess hardness, elastic modulus, and elastic recovery. The Cu:Se = 2.0 sample exhibited the highest hardness but the lowest elastic recovery and elastic modulus from indentation, suggesting strong intragrain cohesion but limited elastic deformation due to fine grain structure. In contrast, the sub-stoichiometric Cu:Se = 1.8 phase displayed higher elastic modulus and recovery, possibly due to a more rigid Se sub-lattice and defect-mediated deformation mechanisms. Compression tests confirmed the higher bulk modulus in the Cu-deficient phase. Bending tests also showed that the Cu-deficient phase exhibited the highest bending modulus, further supporting its enhanced stiffness under elastic deformation. These results highlight the significant role of stoichiometry and crystallite structure in tuning the mechanical response of thermoelectric Cu–Se compounds, with implications for their durability and performance in practical applications. Full article

(This article belongs to the Special Issue Recent Developments of Non-Ferrous Alloys: Processing, Microstructure and Properties (2nd Edition))

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16 pages, 4757 KiB

Open AccessArticle

Effect of Laser Power on the Microstructure and Fracture of Notched IN718 Specimens Fabricated by Laser Powder Bed Fusion

by Naheen Ibn Akbar, Kalyan Nandigama, Ishaan Sati, Bharath Bhushan Ravichander and Golden Kumar

Metals 2025, 15(6), 639; https://doi.org/10.3390/met15060639 - 6 Jun 2025

Abstract

This study examines the impact of laser power on the microstructure and fracture behavior of IN718 specimens fabricated using laser powder bed fusion. Single-edge notched bend specimens were fabricated with varying laser power from 140 W to 260 W, and their fracture behavior [...] Read more.

This study examines the impact of laser power on the microstructure and fracture behavior of IN718 specimens fabricated using laser powder bed fusion. Single-edge notched bend specimens were fabricated with varying laser power from 140 W to 260 W, and their fracture behavior was analyzed following the ASTM E1820-23b standard. The porosity and grain morphology remained unaffected by the presence of a notch parallel to the build direction. An elastic–plastic fracture mechanics approach was used to measure J-R curves, which quantify the energy required for crack propagation. Crack initiation and growth during quasistatic loading were monitored using image analysis. The results revealed a strong correlation between crack initiation and propagation, type of porosity, and relative density. The specimen printed with the optimal laser power of 180 W demonstrated the highest relative density and the greatest resistance to crack propagation. Large non-spherical defects formed due to lack-of-fusion at lower laser power are more detrimental to the crack propagation resistance. Full article

(This article belongs to the Section Additive Manufacturing)

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10 pages, 1472 KiB

Open AccessTechnical Note

Modeling of Tensile Tests Flow Curves Using an Explicit Piecewise Inverse Approach

by Aditya Vuppala, Holger Brüggemann, David Bailly and Emad Scharifi

Metals 2025, 15(6), 638; https://doi.org/10.3390/met15060638 - 5 Jun 2025

Abstract

Tensile tests are a common method for characterizing plastic behavior for sheet metal forming applications. During tensile testing at the beginning of the deformation, the stress state is uniaxial; however, as the deformation proceeds, the state changes to triaxial, making the post-processing of [...] Read more.

Tensile tests are a common method for characterizing plastic behavior for sheet metal forming applications. During tensile testing at the beginning of the deformation, the stress state is uniaxial; however, as the deformation proceeds, the state changes to triaxial, making the post-processing of experimental data challenging using analytical methods. In contrast, inverse approaches in which the behavior is represented by constitutive equations and the parameters are fitted using an iterative procedure are extremely dependent on the empirical equation chosen at the outset and can be computationally expensive. The inverse piecewise flow curve determination method, previously developed for compression tests, is extended in this paper to tensile testing. A stepwise approach is proposed to calculate constant strain rate flow curves accounting for the unique characteristics of tensile deformation. To capture the effects of localized strain rate variations during necking, a parallel flow curve determination strategy is introduced. Tensile test flow curves for manganese-boron steel 22MnB5, a material commonly used in hot stamping applications, are determined, and the approach is demonstrated for virtual force–displacement curves. It has been shown that these curves can replicate the virtual experimental flow curves data with a maximum deviation of 1%. Full article

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23 pages, 4555 KiB

Open AccessArticle

Prediction of Medium-Thick Plates Weld Penetration States in Cold Metal Transfer Plus Pulse Welding Based on Deep Learning Model

by Yanli Song, Kang Song, Yipeng Peng, Lin Hua, Jue Lu and Xuanguo Wang

Metals 2025, 15(6), 637; https://doi.org/10.3390/met15060637 - 5 Jun 2025

Abstract

During the cold metal transfer plus pulse (CMT+P) welding process of medium-thick plates, problems such as incomplete penetration (IP) and burn-through (BT) are prone to occur, and weld pool morphology is important information reflecting the penetration states. In order to acquire high-quality weld [...] Read more.

During the cold metal transfer plus pulse (CMT+P) welding process of medium-thick plates, problems such as incomplete penetration (IP) and burn-through (BT) are prone to occur, and weld pool morphology is important information reflecting the penetration states. In order to acquire high-quality weld pool images under complex welding conditions, such as smoke and arc light, a welding monitoring system was designed. For the purpose of predicting weld penetration states, the improved Inception-ResNet prediction model was proposed. Squeeze-and-Excitation (SE) block was added after each Inception-ResNet block to further extract key feature information from weld pool images, increasing the weight of key features beneficial for predicting the penetration states. The model has been trained, validated, and tested. The results demonstrate that the improved model has an accuracy of over 96% in predicting penetration states of aluminum alloy medium-thick plates compared to the original model. The model was applied in welding experiments and achieved an accurate prediction. Full article

(This article belongs to the Special Issue Advanced Lightweight Materials: Processing, Characterization and Applications)

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Graphical abstract

12 pages, 1670 KiB

Open AccessArticle

Multiphase Identification Through Automatic Classification from Large-Scale Nanoindentation Mapping Compared to an EBSD-Machine Learning Approach

by Carl Slater, Bharath Bandi, Pedram Dastur and Claire Davis

Metals 2025, 15(6), 636; https://doi.org/10.3390/met15060636 - 5 Jun 2025

Abstract

Characterising and quantifying complex multiphase steels is a challenging and time-consuming process, which is often open to subjectivity when based on image analysis of optical metallographic or SEM images. The properties of multiphase steels are highly sensitive to their individual phase properties and [...] Read more.

Characterising and quantifying complex multiphase steels is a challenging and time-consuming process, which is often open to subjectivity when based on image analysis of optical metallographic or SEM images. The properties of multiphase steels are highly sensitive to their individual phase properties and fractions, necessitating the development of robust characterisation tools. This paper presents a method for classifying nanoindentation maps into proportional fractions of up to five distinct microstructural regions in dual-phase and complex-phase steels. The phases/regions considered are ferrite, ferrite containing mobile dislocations, bainite, tempered martensite, and untempered martensite. A range of microstructures with varying fractions of phases were evaluated using both SEM/EBSD and nanoindentation. A machine learning (ML) approach applied to EBSD data showed good consistency in characterising a two-phase system. However, as the microstructural system complexity increased, variations were observed between different analysts and the sensitivity to the ML training data increased when four phases were present (reaching up to ~11% difference in the ferrite phase fraction determined). The proposed nanoindentation mapping technique does not show operator sensitivity and enables the quantification of additional microstructural features, such as identifying and quantifying ferrite regions with a high density of mobile dislocations and the degree of martensite tempering. Full article

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18 pages, 4243 KiB

Open AccessArticle

Characterization of Porosity and Copper Infiltration Mechanism in Sintered Steel via Computed Tomography

by Pengcheng Lin, Linshan Wang, Shuanghua Liang, Xuebing Liang, Qiang Hu, Limin Wang and Xuanhui Qu

Metals 2025, 15(6), 635; https://doi.org/10.3390/met15060635 - 5 Jun 2025

Abstract

This study employs CT non-destructive detection to quantitatively analyze the pore structure of sintered steel and investigate copper infiltration mechanisms. As density increases from 6.55 to 6.95 g/cm³, pore characteristics exhibit significant changes: pore quantity initially increases then decreases, while average [...] Read more.

This study employs CT non-destructive detection to quantitatively analyze the pore structure of sintered steel and investigate copper infiltration mechanisms. As density increases from 6.55 to 6.95 g/cm³, pore characteristics exhibit significant changes: pore quantity initially increases then decreases, while average pore size monotonically reduces from 35.7 to 17.2 μm. Copper infiltration dramatically transforms the material’s porosity, characterized by reduced pore count, decreased distribution uniformity, increased closed pore proportion, and morphological regularization. The infiltration process demonstrates selective filling, primarily governed by pore connectivity, size effect, and capillary forces. Molten copper preferentially penetrates high-connectivity networks, prioritizing irregular angular regions. Medium-sized pores (10.52–23.76 μm) with optimal connectivity are predominantly filled. At 6.75 g/cm³, an optimal balance between pore quantity, size, and connectivity facilitates uniform copper infiltration. Full article

(This article belongs to the Special Issue Powder Metallurgy of Metals and Alloys)

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13 pages, 3783 KiB

Open AccessArticle

Harvesting Reactor Pressure Vessel Beltline Material from the Decommissioned Zion Nuclear Power Plant Unit 1

by Thomas M. Rosseel, Mikhail A. Sokolov, Xiang (Frank) Chen and Randy K. Nanstad

Metals 2025, 15(6), 634; https://doi.org/10.3390/met15060634 - 5 Jun 2025

Abstract

The decommissioning of the Zion Nuclear Power Plant (NPP) provided a unique opportunity to harvest and study service-aged reactor pressure vessel (RPV) beltline materials. This work, conducted through the U.S. Department of Energy’s Light Water Reactor Sustainability (LWRS) Program, aims to improve the [...] Read more.

The decommissioning of the Zion Nuclear Power Plant (NPP) provided a unique opportunity to harvest and study service-aged reactor pressure vessel (RPV) beltline materials. This work, conducted through the U.S. Department of Energy’s Light Water Reactor Sustainability (LWRS) Program, aims to improve the understanding of radiation-induced embrittlement to support extended nuclear plant operations. Material segments containing the Linde 80 flux, wire heat 72105 (WF-70) beltline weld and the A533B Heat B7835-1 base metal, obtained from the intermediate shell region with a peak fluence of 0.7 × 10¹⁹ n/cm² (E > 1.0 MeV), were extracted, cut into blocks, and machined into test specimens for mechanical and microstructural characterization. The segmentation process involved oxy-propane torch-cutting, followed by precision machining using wire saws and electrical discharge machining (EDM). A chemical composition analysis confirmed the expected variations in alloying elements, with copper levels being notably higher in the weld metal. The harvested specimens enable a detailed evaluation of through-wall embrittlement gradients, a comparison with the existing surveillance data, and the validation of predictive embrittlement models. This study provides critical data for assessing long-term reactor vessel integrity, informing aging-management strategies, and supporting regulatory decisions to extend the life of nuclear plants. This article is a revised and expanded version of a paper entitled, “Current Status of the Characterization of RPV Materials Harvested from the Decommissioned Zion Unit 1 Nuclear Power Plant”, PVP2017-65090, which was accepted and presented at the ASME 2017 Pressure Vessels and Piping Conference, Waikoloa, HI, USA, 16–20 July 2017. Full article

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14 pages, 3805 KiB

Open AccessArticle

Continuous Fabrication Process of Aluminum Foam from Foaming to Press Forming

by Yoshihiko Hangai, Yuito Kaneko and Kenji Amagai

Metals 2025, 15(6), 633; https://doi.org/10.3390/met15060633 - 4 Jun 2025

Viewed by 4

Abstract

Aluminum foam is expected to be a leading candidate for lightweight parts due to its light weight and excellent shock-absorption and sound-absorption properties. In order to use it as a part, it is essential to form it into the desired shape. However, the [...] Read more.

Aluminum foam is expected to be a leading candidate for lightweight parts due to its light weight and excellent shock-absorption and sound-absorption properties. In order to use it as a part, it is essential to form it into the desired shape. However, the cell walls that form the pores are composed of thin aluminum. When aluminum foam is formed, the cell walls easily fracture and the pores collapse. This results in the loss of the properties of the aluminum foam. Past studies have shown that press forming aluminum foam immediately after foaming, while it is still in the softened state, prevents cell wall failure and pore deformation. In this study, we attempted to perform a continuous process from the foaming of the precursor to the press forming of aluminum foam for three precursors, for the purpose of the continuous production of aluminum foam with desired shapes. It was shown that it is possible to continuously and sequentially foam the precursors by heating and press forming the foamed samples. In addition, aluminum foam with a similar shape, porosity, and pore structure can be fabricated using the continuous process. Also, it was shown that aluminum foam with complex shapes can also be continuously fabricated by using a complex-shaped die. Furthermore, it was indicated that the use of a die in press forming can shorten the cooling time and reduce the production time. Full article

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20 pages, 3512 KiB

Open AccessReview

Data Science in Order and Disorder of High-Entropy Materials

by Jiasheng Wang, Jianzhong Jiang, Peter K. Liaw, Guihong Geng and Yong Zhang

Metals 2025, 15(6), 632; https://doi.org/10.3390/met15060632 - 3 Jun 2025

Viewed by 50

Abstract

In recent years, high-entropy materials (HEMs) have garnered significant attention due to their unique multi-principal element compositions, which endow them with remarkable properties distinct from traditional materials. The order and disorder in HEMs are particularly complex, influenced by factors such as temperature, pressure, [...] Read more.

In recent years, high-entropy materials (HEMs) have garnered significant attention due to their unique multi-principal element compositions, which endow them with remarkable properties distinct from traditional materials. The order and disorder in HEMs are particularly complex, influenced by factors such as temperature, pressure, and composition, and are closely related to their mechanical and physical properties. This review systematically summarizes the progress in understanding the order and disorder in HEMs, with a focus on the role of data science in this field. We introduce the basic concepts of order and disorder and the related research in HEMs, discuss the nonlinear behaviors of HEMs, and elaborate on the relevant applications of data science, including analysis by machine learning, molecular dynamics simulations, and Monte Carlo simulations. Challenges and future directions are also explored, aiming to provide comprehensive insights into materials science. Full article

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23 pages, 16700 KiB

Open AccessArticle

Influence of Microstructure and Texture on Tensile Properties of an As-Rolled Ti₂AlNb-Based Alloy

by Caihong Jing, Shoujiang Qu, Aihan Feng, Hao Wang and Daolun Chen

Metals 2025, 15(6), 631; https://doi.org/10.3390/met15060631 - 3 Jun 2025

Viewed by 70

Abstract

Ti₂AlNb-based alloys are widely used in aerospace applications due to their excellent high-temperature mechanical properties. This study aims to investigate the texture, microstructural evolution, and phase transformation behavior of Ti₂AlNb-based alloy sheets during heat treatment and their effects on [...] Read more.

Ti₂AlNb-based alloys are widely used in aerospace applications due to their excellent high-temperature mechanical properties. This study aims to investigate the texture, microstructural evolution, and phase transformation behavior of Ti₂AlNb-based alloy sheets during heat treatment and their effects on tensile properties. During heat treatment, B2 → O phase transformation occurs at 550 °C and 650 °C, while Ostwald ripening takes place at 700 °C and 850 °C. The α₂ phase undergoes spheroidization around 1000 °C due to grain boundary separation and recrystallization. Additionally, the B2, O, and α₂ phases all exhibit strong textures. The B2-phase texture follows a cubic orientation ({100}<001>), rotated ~30° around the normal direction (ND). The O-phase texture consists of a strong {100}<010> rolling texture and a weaker texture component <001>//RD, influenced by the B2-phase texture, rolling deformation, and variant selection during O-phase precipitation. Each B2 grain generates four variants, forming distinct O-phase textures within the same grain. The α₂-phase texture exhibits typical rolling textures, [0001]//TD, <

\bar{1}

2

\bar{1}

0>//ND, and {11

\bar{2}

0}<01

\bar{1}

0>, remaining stable after heat treatment. Tensile tests show that the rolled sheet has better ductility along the rolling direction (RD), while the transverse direction (TD) demonstrates higher yield strength (up to 1136 MPa). The anisotropy in tensile properties is mainly attributed to the O-phase texture, with minor contributions from the α₂-phase and B2-phase textures. These findings provide a theoretical basis for optimizing the mechanical properties of Ti₂AlNb-based alloys. Full article

(This article belongs to the Special Issue Numerical Simulation and Experimental Research of Metal Rolling)

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4 pages, 133 KiB

Open AccessEditorial

Advances in Preparation Methods and Numerical Simulation of Composites: Formation and Properties

by Zhengyi Jiang and Hongmei Zhang

Metals 2025, 15(6), 630; https://doi.org/10.3390/met15060630 - 3 Jun 2025

Viewed by 49

Abstract

Advanced composite materials are lightweight, have high strength, and have designable performance [...] Full article

(This article belongs to the Special Issue Advances in Preparation Methods and Numerical Simulation of Composites: Formation and Properties)

25 pages, 3800 KiB

Open AccessArticle

Deformation and Energy Absorption Characteristics of Metallic Thin-Walled Tube with Hierarchical Honeycomb Lattice Infills for Crashworthiness Application

by Shahrukh Alam, Mohammad Uddin and Colin Hall

Metals 2025, 15(6), 629; https://doi.org/10.3390/met15060629 - 2 Jun 2025

Viewed by 258

Abstract

This paper investigates the axial deformation characteristics and crashworthiness of thin-walled metal tubes (TWT) reinforced with Polyetherketoneketone (PEKK) honeycomb lattice structures consisting of bio-inspired hierarchical cellular topological features. Experimentally validated numerical results revealed that the specific energy absorption capacity (SEA) of these composite [...] Read more.

This paper investigates the axial deformation characteristics and crashworthiness of thin-walled metal tubes (TWT) reinforced with Polyetherketoneketone (PEKK) honeycomb lattice structures consisting of bio-inspired hierarchical cellular topological features. Experimentally validated numerical results revealed that the specific energy absorption capacity (SEA) of these composite structures increased with filler volume corresponding to a specific cellular topology. This includes the bio-inspired hierarchical sparse (BHS) topology, which registered a remarkable improvement in SEA over the hollow tube of 202%. In contrast, the central (BHC) topology deformed in an unstable hex-dominated pattern and triggered catastrophic failure of the composite in global bending mode. Furthermore, rigid cells were shown to drastically increase the initial peak force (IPF), while cells with low stiffness were beneficial for maintaining a low level of IPF and moderately improving SEA. Moreover, the rib and wall thickness of the BHS honeycomb cells were suitably tailored to increase the SEA by 2.1%, while simultaneously reducing the IPF by 3.7%. These findings suggest that multi-functional mechanical attributes of PEKK hierarchical honeycomb lattice fillers can mutually benefit thin-walled tubes with superior energy absorption capability and lightweight features over conventional lattice-filled tubes or a hollow tube. Full article

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12 pages, 26078 KiB

Open AccessArticle

The Effect of Mg Content on the Microstructure and Open Porosity of a Porous FeAl Intermetallic Compound

by Weilun Xue, Zhuoxuan Liu, Dongming Liu and Zhigang Xu

Metals 2025, 15(6), 628; https://doi.org/10.3390/met15060628 - 31 May 2025

Viewed by 136

Abstract

In this study, a porous FeAl intermetallic compound with high porosity was synthesized via vacuum sintering using Mg powder as a pore-forming agent, leveraging its high saturated vapor pressure and almost non-reactivity with Fe. The influence of the addition of Mg powder on [...] Read more.

In this study, a porous FeAl intermetallic compound with high porosity was synthesized via vacuum sintering using Mg powder as a pore-forming agent, leveraging its high saturated vapor pressure and almost non-reactivity with Fe. The influence of the addition of Mg powder on pore characteristics and microstructure evolution was systematically investigated. The results indicate that variations in Mg content within sintered compacts exhibit a negligible impact on primary phase composition, with the FeAl phase remaining predominant. However, excessive initial Mg content induces the encapsulation of the FeAl phase by minor Fe₂Al₅ and Al₃Mg₂ phases, compromising the phase’s purity. The porosity positively correlates with Mg content, and porous material with a porosity of 72.8% is obtained (40 at.% of Mg as an additive). Moreover, the pore structure manifests as an interconnected hole morphology. These findings provide valuable insights for further exploration of the design of porous FeAl material and its performance enhancement in emerging applications. Full article

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20 pages, 31391 KiB

Open AccessArticle

Oxide Behavior During Laser Surface Melting

by Tomio Ohtsuki and Petrus Christiaan Pistorius

Metals 2025, 15(6), 627; https://doi.org/10.3390/met15060627 - 31 May 2025

Viewed by 97

Abstract

Parts fabricated by laser powder bed fusion (LPBF) contain oxide inclusions, which can be detrimental to fatigue resistance. Under typical LPBF conditions, the atmosphere contains enough oxygen to oxidize reactive elements such as aluminum and titanium, forming oxides in the parts. In this [...] Read more.

Parts fabricated by laser powder bed fusion (LPBF) contain oxide inclusions, which can be detrimental to fatigue resistance. Under typical LPBF conditions, the atmosphere contains enough oxygen to oxidize reactive elements such as aluminum and titanium, forming oxides in the parts. In this work, mechanisms of oxide formation and oxide alteration were studied by laser-remelting the surfaces of bulk specimens of IN718 and AlSi10Mg, without the addition of metal powder. Calculations based on the mass transfer of oxygen to the melt pool surface indicated that direct oxidation of the melt pool did not play a major role. Rather, both the oxidation of hot spatter and reworking of the pre-existing oxide affected the concentration and morphology of oxides on the metal surface. Full article

(This article belongs to the Special Issue Laser Processing Technology for Metals)

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Graphical abstract

28 pages, 5631 KiB

Open AccessArticle

Dislocation Avalanches in Compressive Creep and Shock Loadings

by Alexander R. Umantsev

Metals 2025, 15(6), 626; https://doi.org/10.3390/met15060626 - 31 May 2025

Viewed by 158

Abstract

Motion of dislocations is a common mechanism of plasticity in many materials. Acoustic emissions and stress bursts turned out to be integral parts of this mechanism. An adequate description of these processes is an important goal of the Materials Theory, which aims to [...] Read more.

Motion of dislocations is a common mechanism of plasticity in many materials. Acoustic emissions and stress bursts turned out to be integral parts of this mechanism. An adequate description of these processes is an important goal of the Materials Theory, which aims to describe the mechanical properties of materials and their reliability in service. In this article, a novel approach to dislocation plasticity capable of describing emission events and stress bursts is introduced, and computational experiments intended to model the processes of compressive creep and shock compression in samples of various makeup and sizes are discussed. It turns out that the emission events self-organize into dislocation avalanches, which propagate at a speed determined by the conditions of loading. In the compressive creep experiments, the avalanches arrange into slow-moving slip bands, while in the shock compression experiments the avalanches move faster than sound. Full article

(This article belongs to the Special Issue Self-Organization in Plasticity of Metals and Alloys)

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13 pages, 3086 KiB

Open AccessArticle

Laser-MIG Hybrid Welding–Brazing Characteristics of Ti/Al Butt Joints with Different Groove Shapes

by Xin Zhao, Zhibin Yang, Yonghao Huang, Taixu Qu, Rui Cheng and Haiting Lv

Metals 2025, 15(6), 625; https://doi.org/10.3390/met15060625 - 31 May 2025

Viewed by 193

Abstract

TC4 titanium alloy and 5083 aluminum alloy with different groove shapes were joined by laser-MIG hybrid welding–brazing using ER4043 filler wire. The effects of groove shape on the weld formation, intermetallic compounds and tensile property of the Ti/Al butt joints were investigated. The [...] Read more.

TC4 titanium alloy and 5083 aluminum alloy with different groove shapes were joined by laser-MIG hybrid welding–brazing using ER4043 filler wire. The effects of groove shape on the weld formation, intermetallic compounds and tensile property of the Ti/Al butt joints were investigated. The welds without obvious defects could be obtained with grooves of I-shape and V-shape on Ti side, while welds quality with grooves of V-shape on Al side and V-shape on both sides were slightly worse. The interfacial intermetallic compounds (IMCs) on the brazing interface were homogeneous in the joints with groove of V-shape on Ti side, and V-shape on both sides, which had similar thickness and were both composed of TiAl₃. Unlike the IMCs mainly composed of TiAl₃ at the I-shape groove interface, TiAl₃, TiAl, and Ti₃Al constituted the IMCs at the V-shape on Al side interface. The average tensile strength of Ti/Al joints with groove of I-shape was the highest at 238 MPa, and was lowest at 140 MPa with groove of V-shape on Al side. The tensile samples mainly fractured at IMCs interface and the fractured surfaces all exhibited mixed brittle–ductile fracture mode. Based on the above research results, I-shape groove was recommended for laser-arc hybrid welding–brazing of 4 mm thick Ti/Al dissimilar butt joints. Full article

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

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11 pages, 10009 KiB

Open AccessArticle

Influence of Welding Speed on the Microstructure and Mechanical Properties of Laser-Welded Joints in 316L Stainless Steel Sheets

by Jianqiang Liu, Yu Nie, Qiaobo Feng, Xiuyu Liang, Haiyang Lei, Sizhe Niu and Ming Lou

Metals 2025, 15(6), 624; https://doi.org/10.3390/met15060624 - 31 May 2025

Viewed by 239

Abstract

This study investigates the effect of welding speed on the microstructure and mechanical properties of pulsed laser lap-welded 0.2 mm 316L stainless steel sheets, commonly used in fuel cell bipolar plates. Welding speeds ranging from 6 to 26 mm/s were tested while other [...] Read more.

This study investigates the effect of welding speed on the microstructure and mechanical properties of pulsed laser lap-welded 0.2 mm 316L stainless steel sheets, commonly used in fuel cell bipolar plates. Welding speeds ranging from 6 to 26 mm/s were tested while other laser parameters remained constant. Results show that increasing welding speed reduces heat input, overlap factor, and weld dimensions. A transition from full to partial penetration occurs beyond 6 mm/s, with no visible heat-affected zone. The weld microstructure features columnar ferrite near fusion boundaries and globular ferrite in the center. Tensile–shear tests reveal that welds maintain higher strength than the base metal up to 22 mm/s, with all fractures occurring in the base material. An optimal speed range of 10–14 mm/s ensures defect-free joints with improved mechanical performance. These findings provide practical guidance for thin-gauge stainless steel welding in fuel cell applications. Full article

(This article belongs to the Special Issue New Welding Materials and Green Joint Technology—2nd Edition)

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24 pages, 1223 KiB

Open AccessArticle

Temperature Dependence of Hardness of High Entropy Alloys

by Ottó K. Temesi, Albert Karacs, Nguyen Q. Chinh and Lajos K. Varga

Metals 2025, 15(6), 623; https://doi.org/10.3390/met15060623 - 30 May 2025

Viewed by 134

Abstract

Correlations have been found for the base value of hardness (as the ratio between the heat of fusion and molar volume) and the softening temperature (as the ratio of heat of fusion and specific heat capacity). The relative change of bulk hardness as [...] Read more.

Correlations have been found for the base value of hardness (as the ratio between the heat of fusion and molar volume) and the softening temperature (as the ratio of heat of fusion and specific heat capacity). The relative change of bulk hardness as a function of temperature, H(T), is studied by three new parametric formulas beside the well-known exponential decay and Arrhenius-type expressions. Mathematically, two formulas can be considered as deriving from the exponential decay; the third one is a new rational fraction expression based on the power of normalized temperature. The normalizing temperature is taken as the softening temperature. In the Arrhenius expression, a temperature-dependent activation energy is introduced, which increases steadily with heating but never surpasses the value of self-diffusion. This rational fracture expression has been shown to be applicable to both pure metals and alloys with arbitrary H(T) curve shapes, from convex (pure metals) to concave (alloys). A detailed description of the fitting of these parametric formulas is given, applying the H(T) data from the literature and from our own measurements. Measuring our refractory high entropy alloy (RHEA) samples, an early softening temperature, smaller than the expected half of the melting point (Ts < Tm/2) was detected, signaling a phase instability in the case of Ti-, Zr- and Hf-containing alloys. Full article

(This article belongs to the Special Issue Feature Papers in Entropic Alloys and Meta-Metals)

15 pages, 3798 KiB

Open AccessArticle

Selective Recovery and Enrichment of Cobalt from Cobalt-Containing Slag by Carbothermal Reduction

by Jiachen Gong, Jian Pan, Jingfu Zhao, Qian Zhang, Guansheng Hao, Yan Liu and Helei Yu

Metals 2025, 15(6), 622; https://doi.org/10.3390/met15060622 - 30 May 2025

Viewed by 130

Abstract

Cobalt ore resources are relatively scarce; thus, the recycling of cobalt-containing slag is highly significant in the economy and society. In this study, the effects of reduction temperature, the reduction agent ratio, reduction time, and particle size on the grade and recovery rate [...] Read more.

Cobalt ore resources are relatively scarce; thus, the recycling of cobalt-containing slag is highly significant in the economy and society. In this study, the effects of reduction temperature, the reduction agent ratio, reduction time, and particle size on the grade and recovery rate of cobalt in a concentrate were systematically investigated during the carbothermal reduction of cobalt-containing slag. The results revealed that the grades of cobalt, iron, and copper in the concentrate after magnetic separation were 4.02%, 2.48%, and 81.33%, respectively, and the recoveries were 94.17%, 74.80%, and 53.27%, respectively, under the reduction temperature of 1150 °C, the reduction agent ratio of 40%, the reduction time of 2 h, and the particle size of −3.0 mm. Furthermore, through static reduction roasting in a muffle furnace and dynamic reduction roasting in a rotary kiln followed by magnetic separation, a stable cobalt grade, high selective recovery, and effective enrichment were achieved under optimal conditions. Full article

(This article belongs to the Special Issue Toward Achieving a Carbon-Neutral Society: Beneficiation and Extractive Metallurgy for Producing Critical Metals from Ores/Wastes)

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21 pages, 6174 KiB

Open AccessArticle

Research on Unidirectional Traveling Wire Electrochemical Discharge Micromachining of Thick Metal Materials

by Rudong Zhang, Xiaocong Tang, Yaowu Zhou, Ying Li and Yongbin Zeng

Metals 2025, 15(6), 621; https://doi.org/10.3390/met15060621 - 30 May 2025

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Abstract

Wire electrochemical discharge machining (WECDM) integrates the effectiveness of electrical discharge machining (EDM) with the superior quality of electrochemical machining (ECM), leading to enhanced machining efficiency, excellent surface finish, and significant potential for advancement. However, previous research has mainly focused on the processing [...] Read more.

Wire electrochemical discharge machining (WECDM) integrates the effectiveness of electrical discharge machining (EDM) with the superior quality of electrochemical machining (ECM), leading to enhanced machining efficiency, excellent surface finish, and significant potential for advancement. However, previous research has mainly focused on the processing of non-metallic materials, with little research in the field of the microfabrication of thick metal materials. The wire electrochemical discharge machining process with large aspect ratios is more complex. Accordingly, a unidirectional traveling wire electrochemical discharge micromachining (UWECDMM) method using a glycol-based electrolyte was proposed. The method employs a glycol solution with low conductivity and a neutral salt, facilitating enhanced mass transfer efficiency through a unidirectional traveling wire, and enabling the realization of high-efficiency, high-precision, and recast-free processing. The phenomenon of discharge in UWECDMM was observed in real-time with a high-speed camera, while the voltage and current waveforms throughout the machining process were carefully analyzed. It was found that electrolysis and discharge alternate. Experiments were conducted to investigate the wire traveling pattern, the recast layer, and the wear of the wire electrode. It was found that due to the small energy of a single discharge, the wear of wire electrodes is minimal after multiple uses and can be reused. Under optimal parameters, a machined surface without a recast layer can be obtained. In the final stages, a standard structure was machined on plates of 10 mm thickness made of pure nickel and 304 stainless steel, using a tungsten wire measuring 30 μm in diameter. The feed rate achieved was 1 μm/s, the surface roughness (Ra) measured 0.06 μm, and the absence of a recast layer confirmed the method’s sustainability and quality traits, indicating significant potential in microfabrication. Full article

(This article belongs to the Special Issue High-Energy Beam Machining of Metals)

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24 pages, 11293 KiB

Open AccessArticle

Optimization of Forming Parameters and Forming Strategy for Stamping of Novel Ultra-Thin Super Ferritic Stainless Steel Bipolar Plates Based on Numerical Simulation

by Jun Lan, Jian Han, Lisong Zhu, Jingwen Song, Meiqing Meng and Zhengyi Jiang

Metals 2025, 15(6), 620; https://doi.org/10.3390/met15060620 - 30 May 2025

Viewed by 114

Abstract

This study investigates the forming process (stamping) of bipolar plates which have applied a novel ultra-thin (0.1 mm) super ferritic stainless steel, i.e., SUS470, whose chromium is sufficiently high for corrosion resistance. A three-dimensional finite element model of the stamping process was developed [...] Read more.

This study investigates the forming process (stamping) of bipolar plates which have applied a novel ultra-thin (0.1 mm) super ferritic stainless steel, i.e., SUS470, whose chromium is sufficiently high for corrosion resistance. A three-dimensional finite element model of the stamping process was developed using the commercial software ABAQUS version 2022. The model incorporated optimized die parameters obtained through Central Composite Design (CCD). This model was used to analyze the effects of key forming parameters, including stamping speed and friction coefficient, on the distribution of stress, strain, and thickness reduction during the stamping process. The finite element modeling (FEM) results disclose that the inner corner of the flow channel is a critical defect-prone region, exhibiting stress concentration, uneven strain distribution, and severe thinning. The optimal forming quality can be achieved at a stamping speed of 100 mm/s and a friction coefficient of 0.185 among all varied options. Further, a comparative study of single-stage, conventional two-stage, and optimized two-stage stamping strategies based on previous investigation demonstrates that the optimized two-stage stamping process can effectively alleviate stress and strain concentrations at the corners, significantly reduce thinning problems, and enhance the uniformity and stability during stamping. In summary, this study provides theoretical support for the design of the forming process (stamping) of high-performance super ferritic stainless steel bipolar plates, which is beneficial to subsequent practical engineering application. Full article

(This article belongs to the Special Issue Modeling, Simulation and Experimental Studies in Metal Forming)

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31 pages, 7884 KiB

Open AccessArticle

Magnetic Pulse Welding of Dissimilar Materials: Weldability Window for AA6082-T6/HC420LA Stacks

by Mario A. Renderos Cartagena, Edurne Iriondo Plaza, Amaia Torregaray Larruscain, Marie B. Touzet-Cortina and Franck A. Girot Mata

Metals 2025, 15(6), 619; https://doi.org/10.3390/met15060619 - 30 May 2025

Viewed by 226

Abstract

Magnetic pulse welding (MPW) is a promising solid-state joining process that utilizes electromagnetic forces to create high-speed, impact-like collisions between two metal components. This welding technique is widely known for its ability to join dissimilar metals, including aluminum, steel, and copper, without the [...] Read more.

Magnetic pulse welding (MPW) is a promising solid-state joining process that utilizes electromagnetic forces to create high-speed, impact-like collisions between two metal components. This welding technique is widely known for its ability to join dissimilar metals, including aluminum, steel, and copper, without the need for additional filler materials or fluxes. MPW offers several advantages, such as minimal heat input, no distortion or warping, and excellent joint strength and integrity. The process is highly efficient, with welding times typically ranging from microseconds to milliseconds, making it suitable for high-volume production applications in sectors including automotive, aerospace, electronics, and various other industries where strong and reliable joints are required. It provides a cost-effective solution for joining lightweight materials, reducing weight and improving fuel efficiency in transportation systems. This contribution concerns an application for the automotive sector (body-in-white) and specifically examines the welding of AA6082-T6 aluminum alloy with HC420LA cold-rolled micro-alloyed steel. One of the main aspects for MPW optimization is the determination of the process window that does not depend on the equipment used but rather on the parameters associated with the physical mechanisms of the process. It was demonstrated that process windows based on contact angle versus output voltage diagrams can be of interest for production use for a given component (shock absorbers, suspension struts, chassis components, instrument panel beams, next-generation crash boxes, etc.). The process window based on impact pressures versus impact velocity for different impact angles, in addition to not depending on the equipment, allows highlighting other factors such as the pressure welding threshold for different temperatures in the impact zone, critical transition speeds for straight or wavy interface formation, and the jetting/no jetting effect transition. Experimental results demonstrated that optimal welding conditions are achieved with impact velocities between 900 and 1200 m/s, impact pressures of 3000–4000 MPa, and impact angles ranging from 18–35°. These conditions correspond to optimal technological parameters including gaps of 1.5–2 mm and output voltages between 7.5 and 8.5 kV. Successful welds require mean energy values above 20 kJ and weld specific energy values exceeding 150 kJ/m². The study establishes critical failure thresholds: welds consistently failed when gap distances exceeded 3 mm, output voltage dropped below 5.5 kV, or impact pressures fell below 2000 MPa. To determine these impact parameters, relationships based on Buckingham’s π theorem provide a viable solution closely aligned with experimental reality. Additionally, shear tests were conducted to determine weld cohesion, enabling the integration of mechanical resistance isovalues into the process window. The findings reveal an inverse relationship between impact angle and weld specific energy, with higher impact velocities producing thicker intermetallic compounds (IMCs), emphasizing the need for careful parameter optimization to balance weld strength and IMC formation. Full article

(This article belongs to the Topic Welding Experiment and Simulation)

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10 pages, 3299 KiB

Open AccessArticle

Superstrength of Nanostructured Ti Grade 4 with Grain Boundary Segregations

by Emil I. Usmanov, Michail Yu. Gutkin, Yinxing Wu, Gang Sha and Ruslan Z. Valiev

Metals 2025, 15(6), 618; https://doi.org/10.3390/met15060618 - 30 May 2025

Viewed by 153

Abstract

Severe plastic deformation and subsequent heat treatments yield nanostructured commercially pure (CP) titanium Grade 4 with average grain size of about 100 nm and exceptional strength. To elucidate the underlying strengthening mechanisms in this nanotitanium (nanoTi), this study uses atom probe tomography (APT) [...] Read more.

Severe plastic deformation and subsequent heat treatments yield nanostructured commercially pure (CP) titanium Grade 4 with average grain size of about 100 nm and exceptional strength. To elucidate the underlying strengthening mechanisms in this nanotitanium (nanoTi), this study uses atom probe tomography (APT) to analyze the atomic structure of grain boundaries and assess impurity segregation. Results reveal the formation of grain boundary segregations, primarily composed of iron (Fe) atoms, reaching concentrations up to 3.3 ± 0.2 at% in localized regions. The average width of these segregation layers is 6.13 ± 0.45 nm. The paper considers a mechanism for forming these segregations and discusses relevant theoretical models describing their contribution to the material’s enhanced strength. Full article

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22 pages, 4656 KiB

Open AccessArticle

Optimization of Sustainable Copper Leaching Using Glycine and Oxidizing Agents in an Alkaline Medium

by Jesús I. Martínez, Aislinn M. Teja, Martín Reyes, Norman Toro, Gabriel Cisneros, Uriel M. Flores, Miguel Pérez Labra, Gustavo Urbano and Julio C. Juarez

Metals 2025, 15(6), 617; https://doi.org/10.3390/met15060617 - 30 May 2025

Viewed by 243

Abstract

The increasing global demand for copper has driven the search for more efficient and sustainable extraction methods, particularly due to the environmental concerns associated with conventional processes. This study investigated the leaching of copper minerals MC (Cu₂O) and malachite (Cu₂ [...] Read more.

The increasing global demand for copper has driven the search for more efficient and sustainable extraction methods, particularly due to the environmental concerns associated with conventional processes. This study investigated the leaching of copper minerals MC (Cu₂O) and malachite (Cu₂CO₃(OH)₂) using glycine as an organic ligand in an alkaline medium, and evaluated the efficiency of hydrogen peroxide (H₂O₂) and ozone (O₃) as oxidizing agents. Chemical and mineralogical characterization using XRD, XRF, ICP, and SEM confirmed the predominance of MC and malachite, along with secondary phases such as hematite and calcite. Leaching experiments were carried out by varying glycine and oxidant concentrations at pH 10, with a reaction time of 240 min, agitation at 800 min⁻¹, a solution volume of 300 mL, and a mineral sample concentration of 0.33 g·L⁻¹. The results showed that O₃ exhibited low efficiency due to its limited solubility, whereas H₂O₂ achieved dissolution rates of 69.7% for MC in 150 min and 96.3% for MMin just 60 min. The glycine-H₂O₂ system optimized reaction time by 84% compared to conventional methods, emerging as a sustainable alternative due to the low toxicity and biodegradability of glycine. Full article

(This article belongs to the Special Issue Current Trends in Non-Ferrous Metals Extraction, Separation, and Refining)

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4 pages, 1565 KiB

Open AccessCorrection

Correction: Lian et al. Microstructure and Mechanical Property of Mg-3Al-1Zn Magnesium Alloy Sheet Processed by Integrated High Temperature Rolling and Continuous Bending. Metals 2020, 10, 380

by Yong Lian, Benhong Liao, Tao Zhou, Wenjun Ge, Laixin Shi, Li Hu, Mingbo Yang and Jin Zhang

Metals 2025, 15(6), 616; https://doi.org/10.3390/met15060616 - 30 May 2025

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Abstract

In the original publication, there were mistakes in Figures 2d, 3, 4b, 5, 6d and 7b as published [...] Full article

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17 pages, 5788 KiB

Open AccessArticle

Hot Isostatic Pressing Synthesis of Al-Ta Energetic Structural Material Based on Modified Drucker–Prager Cap Model

by Zenglin Yang, Pengjie Zhang, Xiaodong Yu, Xianjin Ning and Chengwen Tan

Metals 2025, 15(6), 615; https://doi.org/10.3390/met15060615 - 29 May 2025

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Abstract

The Al-Ta energetic structural material (ESM) has significant potential for applications in energetic fragments. To rationally design the hot isostatic pressing (HIP) process for Al-Ta, this paper developed a novel parameter identification method for the modified Drucker–Prager Cap (DPC) model. The identified parameters [...] Read more.

The Al-Ta energetic structural material (ESM) has significant potential for applications in energetic fragments. To rationally design the hot isostatic pressing (HIP) process for Al-Ta, this paper developed a novel parameter identification method for the modified Drucker–Prager Cap (DPC) model. The identified parameters were subsequently applied to simulate the densification behavior of Al/Ta mixed powders during HIP. Based on the simulation results, the HIP process parameters for fabricating the Al-Ta ESM were determined. Meanwhile, the microstructure, mechanical properties, and impact-induced reaction characteristics of the HIP-fabricated Al-Ta ESM were further analyzed. The main results are as follows. The comparison between the HIP simulations and experiments revealed good agreement, confirming the high accuracy of the identification of the modified DPC model parameters. In addition, the Al-Ta ESM fabricated via HIP at 460 °C/140 MPa/2 h exhibits a dense microstructure and enhanced mechanical properties. Furthermore, it demonstrates effective damage performance during the penetration of double-layered targets. Full article

(This article belongs to the Special Issue Deformation Behavior and Microstructure Evolution of Alloys)

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24 pages, 13221 KiB

Open AccessArticle

Initial Characterization of the Layer Interface for Graphite-Free Additive Friction Stir Deposition of AA7075

by Jacob Hansen, Andrew Holladay, Luk Dean, Aaron Christiansen, Michael Merrell, Yuri Hovanski and Scott Rose

Metals 2025, 15(6), 614; https://doi.org/10.3390/met15060614 - 29 May 2025

Viewed by 168

Abstract

Additive friction stir deposition (AFSD) is a novel friction stir technology. It is one of the most prolific solid-state metal deposition processes. In recent years, the aerospace and defense industries have increased their investment in the deposition of 7xxx aluminum alloys. This has [...] Read more.

Additive friction stir deposition (AFSD) is a novel friction stir technology. It is one of the most prolific solid-state metal deposition processes. In recent years, the aerospace and defense industries have increased their investment in the deposition of 7xxx aluminum alloys. This has allowed AFSDs of 7xxx aluminum to move from a laboratory environment to being tested in an industrial setting. This work strives to help move the AFSD of AA7075 toward an effective production environment by providing an initial characterization of the graphite-free layer interface. To the authors’ knowledge, this is the first graphite-free study to utilize both knub–scroll and scroll tools in AA7075. It is also the first study to compare how flat, knub, knub–scroll, and scroll influence layer mixing in graphite-free AA7075. The condition of the layer interface is particularly important to build direction properties. As many end users of AFSD desire isotropic properties, improving build direction properties is extremely important. This work looks at how external tool geometries and layer height impact the layer interface. The objective is to not only better characterize the layer interface but also to determine if a specific external geometry and or layer height could help facilitate a stronger layer interface. It was found that depositions made by the knub tool at a 2.5 mm layer height generated the most visually consolidated layer interface at an optical and SEM level. Under EDS analysis, the knub tool only saw a 12% variation between peak and background oxygen counts. EBSD scans also revealed a more consistent grain size distribution. Full article

(This article belongs to the Special Issue Advanced Manufacturing Technologies: Friction Stir Welding and Additive Manufacturing of Metals)

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14 pages, 13464 KiB

Open AccessArticle

The Design and Microstructure Evolution Mechanism of New Cr_1.3Ni₂TiAl, CoCr_1.5NiTi_1.5Al_0.2, and V_0.3CoCr_1.2NiTi_1.1Al_0.2 Eutectic High-Entropy Alloys

by Xin Zhang, Haitao Yan, Yao Xiao, Wenxin Feng and Yangchuan Cai

Metals 2025, 15(6), 613; https://doi.org/10.3390/met15060613 - 29 May 2025

Viewed by 178

Abstract

To expand the fundamental understanding of eutectic high-entropy alloys (EHEAs), three novel alloy systems—Cr_1.3Ni₂TiAl, CoCr_1.5NiTi_1.5Al_0.2, and V_0.3CoCr_1.2NiTi_1.1Al_0.2—were rationally designed through synergistic phase diagram analysis and [...] Read more.

To expand the fundamental understanding of eutectic high-entropy alloys (EHEAs), three novel alloy systems—Cr_1.3Ni₂TiAl, CoCr_1.5NiTi_1.5Al_0.2, and V_0.3CoCr_1.2NiTi_1.1Al_0.2—were rationally designed through synergistic phase diagram analysis and thermodynamic parameter calculations. Comprehensive microstructural characterization coupled with mechanical property evaluation revealed that these alloys possess FCC+BCC dual-phase architectures with atypical irregular eutectic morphologies. Notably, progressive microstructural evolution was observed, including amplified grain boundary density and the emergence of brittle nanoscale precipitates. Mechanical testing demonstrated superior compressive yield strengths in these alloys compared to conventional FCC+BCC EHEAs with ordered eutectic structures, albeit accompanied by reduced fracture strain. The Cr_1.3Ni₂TiAl alloy exhibited optimal ductility, with a maximum fracture strain of 15.6%, while V_0.3CoCr_1.2NiTi_1.1Al_0.2 achieved peak strength, with a compressive yield strength of 1389.5 MPa. Multiscale analysis suggests that the enhanced mechanical performance arises from the synergistic interplay between irregular eutectic configurations, expanded grain boundary area, and precipitation strengthening mechanisms. Full article

(This article belongs to the Topic Microstructure and Properties in Metals and Alloys, 3rd Volume)

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23 pages, 6167 KiB

Open AccessArticle

Microstructural Characterization of Martensitic Stainless Steel Blades Manufactured by Directed Energy Deposition (DED)

by Caroline Cristine de Andrade Ferreira, Rafael Humberto Mota de Siqueira, Johan Grass Nuñez, Fábio Edson Mariani, Reginaldo Teixeira Coelho, Daolun Chen and Milton Sérgio Fernandes de Lima

Metals 2025, 15(6), 612; https://doi.org/10.3390/met15060612 - 29 May 2025

Viewed by 257

Abstract

This study explores the feasibility of manufacturing martensitic stainless steel turbine blades via a directed energy deposition (DED) process using a powder precursor. Five different blade geometries were fabricated using AISI 431 L martensitic stainless steel deposited onto an AISI 304 L austenitic [...] Read more.

This study explores the feasibility of manufacturing martensitic stainless steel turbine blades via a directed energy deposition (DED) process using a powder precursor. Five different blade geometries were fabricated using AISI 431 L martensitic stainless steel deposited onto an AISI 304 L austenitic stainless steel substrate. The produced components were characterized in terms of microstructure, surface roughness, porosity, hardness, and residual stresses in both the as-processed condition and after heat treatment at 260 and 593 °C. Optical and scanning electron microscopy (SEM) analyses revealed a predominantly martensitic microstructure with well-defined grain boundaries. Heat treatment influenced the phase distribution and grain size, but did not have a significant impact on the surface roughness or modulus of elasticity. Tomographic assessments confirmed the absence of aligned or coalesced pores, which are critical sites for crack initiation. Residual stress analysis indicated the presence of compressive stresses in all blade geometries, which were effectively relieved by heat treatment. In addition, salt spray corrosion tests demonstrated that the corrosion resistance of the manufactured blades was similar to that of the base material. These findings suggest that DED is a viable technique for producing and repairing turbine blades, providing structural integrity and mechanical properties suitable for high-performance applications. Full article

(This article belongs to the Special Issue Laser, Plasma and Radiation Processing of Metals, Alloys, and Composite Materials)

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13 pages, 2082 KiB

Open AccessArticle

Laser–Arc Welding Adaptive Model of Multi-Pre-Welding Condition Based on GA-BP Neural Network

by Zesheng Wu, Zhaodong Zhang and Gang Song

Metals 2025, 15(6), 611; https://doi.org/10.3390/met15060611 - 28 May 2025

Viewed by 224

Abstract

In large welding structures, maintaining a uniform assembly condition and machined dimension in the pre-welding groove is challenging. The assembly condition and machined dimension of the pre-welding groove significantly impact the selection of the welding parameters. In this study, laser–arc hybrid welding is [...] Read more.

In large welding structures, maintaining a uniform assembly condition and machined dimension in the pre-welding groove is challenging. The assembly condition and machined dimension of the pre-welding groove significantly impact the selection of the welding parameters. In this study, laser–arc hybrid welding is used to perform butt welding on 6 mm Q345 steel in various assembly conditions, and we propose an adaptive model of the BP neural network optimized by a genetic algorithm (GA) for laser–arc welding. By employing the GA algorithm to optimize the parameters of the neural network, the relationship between the pre-welding groove parameters and welding parameters is established. The mean square error (MSE) of the GA-BP neural network is 0.75%. It is verified via experiments that the neural network can predict the welding parameters required to process a specific welding morphology under different pre-welding grooves. This model provides technical support for the development of intelligent welding systems for large and complex components. Full article

(This article belongs to the Special Issue Advances in Welding and Joining of Alloys and Steel)

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