To achieve crack repair in a Ni-based single-crystal alloy, a GH4738 repairing layer was cladded onto the surface of the single-crystal DD5 alloy using the laser cladding method. The effects of the laser power and scanning speed on the microstructures and mechanical properties of the repaired sample were studied. The results showed that the typical γ/γ′ phases and carbide were formed in both the repairing layer and substrate, and the carbide primarily belonged to the Ta-rich compound. An increase in the cladding power caused the repairing layer to crack. When the laser power was 1200 W and the cladding speed was 2 mm/s, the tensile strength and elongation of the repaired sample were 1126.1 MPa and 12.2 %, respectively. The fracture mechanism was primarily a cleavage fracture. The grain growth direction of the repairing layer tended toward the [001] direction, and no noticeable difference in the orientation from that of the substrate was observed. The lattice mismatch between the phase interface of the repairing layer and substrate was small. This indicated that the growth of the γ/γ′ phases between these two regions maintained a coherent relationship, which was the primary reason for the excellent mechanical properties of the repaired samples.
{"title":"Enhancement of the mechanical properties of nickel-based single-crystal alloy based on near [001]-oriented growth microstructures via laser cladding","authors":"Zhi-Sheng Nong, Han-Sheng Zhi, Xue Cui, Qian-Gang Xu, Rong-Zheng Xu, Moliar Oleksandr","doi":"10.1016/j.msea.2025.148233","DOIUrl":"10.1016/j.msea.2025.148233","url":null,"abstract":"<div><div>To achieve crack repair in a Ni-based single-crystal alloy, a GH4738 repairing layer was cladded onto the surface of the single-crystal DD5 alloy using the laser cladding method. The effects of the laser power and scanning speed on the microstructures and mechanical properties of the repaired sample were studied. The results showed that the typical γ/γ′ phases and carbide were formed in both the repairing layer and substrate, and the carbide primarily belonged to the Ta-rich compound. An increase in the cladding power caused the repairing layer to crack. When the laser power was 1200 W and the cladding speed was 2 mm/s, the tensile strength and elongation of the repaired sample were 1126.1 MPa and 12.2 %, respectively. The fracture mechanism was primarily a cleavage fracture. The grain growth direction of the repairing layer tended toward the [001] direction, and no noticeable difference in the orientation from that of the substrate was observed. The lattice mismatch between the phase interface of the repairing layer and substrate was small. This indicated that the growth of the γ/γ′ phases between these two regions maintained a coherent relationship, which was the primary reason for the excellent mechanical properties of the repaired samples.</div></div>","PeriodicalId":385,"journal":{"name":"Materials Science and Engineering: A","volume":"931 ","pages":"Article 148233"},"PeriodicalIF":6.1,"publicationDate":"2025-03-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143683507","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-03-18DOI: 10.1016/j.msea.2025.148186
David Montes de Oca Zapiain, Nicole K. Aragon, Hojun Lim
Voids have a significant impact on the structural safety and performance of polycrystalline metal alloys given their crucial role on the initiation and evolution of damage. Therefore, a fundamental understanding of the relationship between the internal crystalline structure of metal alloys and their corresponding damage behavior and properties is essential for the materials community. Crystal plasticity theories, in conjunction with finite element (CPFEM), are actively used to describe and characterize this behavior given the fact that they directly consider the orientation of the crystallographic plains, slip systems and other microstructural features. Nevertheless, despite its accuracy, CPFEM-based analysis protocols are often ill-suited for establishing a computationally efficient and accurate linkage between the microstructure and the resulting damage performance given their high computational cost and their need to iteratively solve complex, numerically stiff and highly non-linear equations. In this work, we address this challenge by establishing a machine learning (ML)-based linkage between the microstructure and the resulting damage performance. Specifically, we leverage AdaBoosted decision trees to connect crystal orientations, represented with Generalized Spherical Harmonics, to a measure of damage derived from the classical Lemaitre continuum damage model. The developed ML model accurately predicts the Lemaitre stress around a spherical void at a fraction of the computational cost compared to CPFEM simulations.
{"title":"Data-driven quantification of orientation dependent damage caused by voids using Machine Learning","authors":"David Montes de Oca Zapiain, Nicole K. Aragon, Hojun Lim","doi":"10.1016/j.msea.2025.148186","DOIUrl":"10.1016/j.msea.2025.148186","url":null,"abstract":"<div><div>Voids have a significant impact on the structural safety and performance of polycrystalline metal alloys given their crucial role on the initiation and evolution of damage. Therefore, a fundamental understanding of the relationship between the internal crystalline structure of metal alloys and their corresponding damage behavior and properties is essential for the materials community. Crystal plasticity theories, in conjunction with finite element (CPFEM), are actively used to describe and characterize this behavior given the fact that they directly consider the orientation of the crystallographic plains, slip systems and other microstructural features. Nevertheless, despite its accuracy, CPFEM-based analysis protocols are often ill-suited for establishing a computationally efficient and accurate linkage between the microstructure and the resulting damage performance given their high computational cost and their need to iteratively solve complex, numerically stiff and highly non-linear equations. In this work, we address this challenge by establishing a machine learning (ML)-based linkage between the microstructure and the resulting damage performance. Specifically, we leverage AdaBoosted decision trees to connect crystal orientations, represented with Generalized Spherical Harmonics, to a measure of damage derived from the classical Lemaitre continuum damage model. The developed ML model accurately predicts the Lemaitre stress around a spherical void at a fraction of the computational cost compared to CPFEM simulations.</div></div>","PeriodicalId":385,"journal":{"name":"Materials Science and Engineering: A","volume":"931 ","pages":"Article 148186"},"PeriodicalIF":6.1,"publicationDate":"2025-03-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143643535","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Balloon-expandable stents are deployed using radiography, necessitating materials with high X-ray visibility, excellent corrosion resistance, high strength and ductility, and low yield stress. In this study, we designed and developed Co-Cr-W-Pt alloys by replacing Ni with Pt in a Co-Cr-W-Ni (ASTM F90, L605) alloy, which is used for practical balloon-expandable stents, with the aim of achieving both high X-ray visibility and excellent mechanical properties. The brightness of the developed alloys, which was evaluated using an X-ray television system, decreased with an increase in the Pt content, indicating that Pt addition improved X-ray visibility. The developed Co-Cr-W-Pt alloys with grain sizes of 25–48 μm exhibited ductility similar to that of conventional Pt-Cr steel and ultimate tensile strength higher than that of Pt-Cr steel. Anodic-polarization tests revealed that the corrosion resistance of the Co-Cr-W-Pt alloys was comparable to that of the L605 alloy. The elution of metal ions in the simulated body fluid was decreased to an acceptable level, and the developed alloys exhibited lower magnetic susceptibility than the L605 alloy. The Co-Cr-W-Pt alloys with high X-ray visibility, excellent mechanical properties, high corrosion resistance, and low magnetic susceptibility are suitable materials for next-generation balloon-expandable stents.
{"title":"Co-Cr-W-Pt alloys with high X-ray visibility for next-generation balloon-expandable stents","authors":"Tomoki Nakajima , Yuri Ito , Kosuke Ueki , Tomokazu Numano , Kyosuke Ueda , Takayuki Narushima","doi":"10.1016/j.msea.2025.148216","DOIUrl":"10.1016/j.msea.2025.148216","url":null,"abstract":"<div><div>Balloon-expandable stents are deployed using radiography, necessitating materials with high X-ray visibility, excellent corrosion resistance, high strength and ductility, and low yield stress. In this study, we designed and developed Co-Cr-W-Pt alloys by replacing Ni with Pt in a Co-Cr-W-Ni (ASTM <span><span>F90</span><svg><path></path></svg></span>, <span><span>L605</span><svg><path></path></svg></span>) alloy, which is used for practical balloon-expandable stents, with the aim of achieving both high X-ray visibility and excellent mechanical properties. The brightness of the developed alloys, which was evaluated using an X-ray television system, decreased with an increase in the Pt content, indicating that Pt addition improved X-ray visibility. The developed Co-Cr-W-Pt alloys with grain sizes of 25–48 μm exhibited ductility similar to that of conventional Pt-Cr steel and ultimate tensile strength higher than that of Pt-Cr steel. Anodic-polarization tests revealed that the corrosion resistance of the Co-Cr-W-Pt alloys was comparable to that of the L605 alloy. The elution of metal ions in the simulated body fluid was decreased to an acceptable level, and the developed alloys exhibited lower magnetic susceptibility than the L605 alloy. The Co-Cr-W-Pt alloys with high X-ray visibility, excellent mechanical properties, high corrosion resistance, and low magnetic susceptibility are suitable materials for next-generation balloon-expandable stents.</div></div>","PeriodicalId":385,"journal":{"name":"Materials Science and Engineering: A","volume":"931 ","pages":"Article 148216"},"PeriodicalIF":6.1,"publicationDate":"2025-03-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143683035","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
HWTS 50 is a Cr, Mo, V is a new lean hot work tool steel with ∼0.2 wt% carbon, designed with chemical composition modifications to achieve comparable properties and temper resistance to those of medium carbon hot work tool steels such as AISI H13 (∼0.4 % C in wt.), while offering improved processability in laser additive manufacturing (LAM) processes. This paper reports on the processing and properties of this tool steel by laser-directed energy deposition (L-DED). Results suggest achievement of near-fully dense and crack-free martensitic microstructure with up to 6 vol% retained austenite (RA), which is substantially lower than that typically found in laser AM-processed AISI H13 (i.e., up to 20 vol%). As-built (AB) material exhibits a hardness of ∼47 HRC and Charpy V-notch impact energy of ∼20 J. Hardness of 48–50 HRC can be achieved by tempering slightly above the secondary hardness peak of 575 °C, either through quenching and tempering or direct double tempering from AB condition. Direct tempering improves temper resistance due to higher dislocation density and higher matrix supersaturation in elements carbon, nitrogen, and vanadium in AB condition, leading to a higher number density of fine and stable secondary carbides through over-tempering. In the above hardness range, the impact toughness of quenched and tempered steel was substantially higher than that of directly tempered one (i.e., ∼18 J vs. ∼12 J). Increased impact energy by prior quenching could be ascribed to microstructural homogenization, removal of inter-dendritic micro-segregation, and columnar prior austenite grain boundaries, which act as preferential sites for chains of alloy carbides precipitation, serving as low energy preferential crack initiation and propagation path. The new steel grade showed enhanced tempering resistance compared to AISI H13, particularly at elevated temperatures (i.e., >600 °C). Enhanced AM processability, optimum balance of hardness-, impact toughness-, and tempering resistance suggest it can be used for the manufacturing and repair of hot work tool steels in laser AM processes.
{"title":"Laser-directed energy deposition additive manufacturing of a lean hot work tool steel: Tempering behavior and impact toughness","authors":"Zhao Zhao , Lorena Emanuelli , Sasan Amirabdollahian , Giorgia Lupi , Riccardo Casati , Faraz Deirmina , Massimo Pellizzari","doi":"10.1016/j.msea.2025.148220","DOIUrl":"10.1016/j.msea.2025.148220","url":null,"abstract":"<div><div>HWTS 50 is a Cr, Mo, V is a new lean hot work tool steel with ∼0.2 wt% carbon, designed with chemical composition modifications to achieve comparable properties and temper resistance to those of medium carbon hot work tool steels such as AISI H13 (∼0.4 % C in wt.), while offering improved processability in laser additive manufacturing (LAM) processes. This paper reports on the processing and properties of this tool steel by laser-directed energy deposition (L-DED). Results suggest achievement of near-fully dense and crack-free martensitic microstructure with up to 6 vol% retained austenite (RA), which is substantially lower than that typically found in laser AM-processed AISI H13 (i.e., up to 20 vol%). As-built (AB) material exhibits a hardness of ∼47 HRC and Charpy V-notch impact energy of ∼20 J. Hardness of 48–50 HRC can be achieved by tempering slightly above the secondary hardness peak of 575 °C, either through quenching and tempering or direct double tempering from AB condition. Direct tempering improves temper resistance due to higher dislocation density and higher matrix supersaturation in elements carbon, nitrogen, and vanadium in AB condition, leading to a higher number density of fine and stable secondary carbides through over-tempering. In the above hardness range, the impact toughness of quenched and tempered steel was substantially higher than that of directly tempered one (i.e., ∼18 J vs. ∼12 J). Increased impact energy by prior quenching could be ascribed to microstructural homogenization, removal of inter-dendritic micro-segregation, and columnar prior austenite grain boundaries, which act as preferential sites for chains of alloy carbides precipitation, serving as low energy preferential crack initiation and propagation path. The new steel grade showed enhanced tempering resistance compared to AISI H13, particularly at elevated temperatures (i.e., >600 °C). Enhanced AM processability, optimum balance of hardness-, impact toughness-, and tempering resistance suggest it can be used for the manufacturing and repair of hot work tool steels in laser AM processes.</div></div>","PeriodicalId":385,"journal":{"name":"Materials Science and Engineering: A","volume":"931 ","pages":"Article 148220"},"PeriodicalIF":6.1,"publicationDate":"2025-03-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143683101","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-03-17DOI: 10.1016/j.msea.2025.148224
Mustafa Tobah , Zenan Zhang , Mohsen Taheri Andani , Arkajit Ghosh , Amit Misra
Additive manufacturing (AM) of Fe-Cr-Ni alloys via powder bed fusion - laser beam (PBF-LB) was performed on three different powder mixtures with ratios of 30:70, 50:50, and 70:30 (weight %) austenitic stainless steel (SS) 316L and duplex stainless steel (DSS) 2507. Extraordinary room temperature tensile behavior in the as-built state is correlated with the complex microstructures achieved in the mixed powder deposits that are not observed with only SS 316L or DSS 2507 powders. Polycrystalline ferritic microstructures in the 50(316L):50(DSS2507) powder mixture build containing a low volume fraction of ultra-fine scale austenite at grain boundaries has exhibited tensile strength exceeding 1 GPa with elongation to failure of ≈28 % due to enhanced Hall-Petch strengthening coefficient. Additionally, the 70:30 sample showed similar ductility to the 100 % 316L sample (∼34 % and ∼35 % elongation to failure, respectively) despite having ∼65 % ferrite in its microstructure. The retention of ductility in spite of the significant increase in tensile strength, from 410 MPa for 100 % 316L to 764 MPa for the 70 (316L):30(DSS2507) powder mixture build sample is attributed to a twin induced plasticity (TWIP) type effect in the needle-like austenite distributed within the ferrite grains. The strength, strain hardening, and ductility of the different microstructures are analyzed using dislocation theory, based on transmission electron microscopy characterization of deformation mechanisms.
{"title":"Deformation mechanisms of multiphase microstructures in laser powder bed fusion processed stainless steels","authors":"Mustafa Tobah , Zenan Zhang , Mohsen Taheri Andani , Arkajit Ghosh , Amit Misra","doi":"10.1016/j.msea.2025.148224","DOIUrl":"10.1016/j.msea.2025.148224","url":null,"abstract":"<div><div>Additive manufacturing (AM) of Fe-Cr-Ni alloys via powder bed fusion - laser beam (PBF-LB) was performed on three different powder mixtures with ratios of 30:70, 50:50, and 70:30 (weight %) austenitic stainless steel (SS) 316L and duplex stainless steel (DSS) 2507. Extraordinary room temperature tensile behavior in the as-built state is correlated with the complex microstructures achieved in the mixed powder deposits that are not observed with only SS 316L or DSS 2507 powders. Polycrystalline ferritic microstructures in the 50(316L):50(DSS2507) powder mixture build containing a low volume fraction of ultra-fine scale austenite at grain boundaries has exhibited tensile strength exceeding 1 GPa with elongation to failure of ≈28 % due to enhanced Hall-Petch strengthening coefficient. Additionally, the 70:30 sample showed similar ductility to the 100 % 316L sample (∼34 % and ∼35 % elongation to failure, respectively) despite having ∼65 % ferrite in its microstructure. The retention of ductility in spite of the significant increase in tensile strength, from 410 MPa for 100 % 316L to 764 MPa for the 70 (316L):30(DSS2507) powder mixture build sample is attributed to a twin induced plasticity (TWIP) type effect in the needle-like austenite distributed within the ferrite grains. The strength, strain hardening, and ductility of the different microstructures are analyzed using dislocation theory, based on transmission electron microscopy characterization of deformation mechanisms.</div></div>","PeriodicalId":385,"journal":{"name":"Materials Science and Engineering: A","volume":"931 ","pages":"Article 148224"},"PeriodicalIF":6.1,"publicationDate":"2025-03-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143683506","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-03-17DOI: 10.1016/j.msea.2025.148198
Chengsi Zheng , Chengcheng Yu , Yuehua Sun , Shilei Li , Mingya Zhang , Li Liu , Ji Sun
The microstructure-dependent mechanism underlying the phenomenon of high tensile performance accompanied by serrated flow remains unclear in medium-manganese (medium-Mn) steel. This is primarily due to the conventional dynamic strain aging (DSA) theory, which focuses on the effect of carbon atoms while largely neglecting the influence of austenite characteristics. In this study, 0.06C-9Mn steel with varying austenite microstructures was fabricated through different rolling and annealing processes. The correlation between discontinuous and continuous mechanical behavior and austenite characteristics was investigated through microstructural characterization, local and global strain and kinetics measurements, and analytical modeling. To elucidate the microstructure-dependent discontinuous and continuous mechanical behavior of medium-Mn steel, two key parameters were introduced: the effective carbon content for pinning mobile dislocations (XE) and the intensity coefficient of the TRIP effect (TE), both of which were influenced by grain size and initial dislocation density under a given austenite volume fraction. An increase in grain size and initial dislocation density of austenite resulted in a decrease in XE and an increase in TE, with serrated flow emerging once the XE-TE balance reached a critical state. This phenomenon may be attributed to the activation of the DSA mechanism, where a weakened dislocation pinning ability is counteracted by enhanced dislocation mobility driven by the TRIP effect. Furthermore, an increase in TE contributed to improved tensile performance in medium-Mn steel, leading to high tensile strength accompanied by serrated flow. Additionally, the discontinuous stepwise kinetics of strain-induced α′-martensite (SIMα′) transformation was accurately described using an analytical model based on strain surges or localization at the observation site as the PLC band propagated. These findings provide deeper insight into the mechanical behavior of medium-Mn steel and offer a pathway to achieving an optimized strength-elongation balance with minimized serrated flow.
{"title":"Correlation between discontinuous and continuous mechanical behavior and austenite microstructure in 0.06C-9Mn medium-manganese steel","authors":"Chengsi Zheng , Chengcheng Yu , Yuehua Sun , Shilei Li , Mingya Zhang , Li Liu , Ji Sun","doi":"10.1016/j.msea.2025.148198","DOIUrl":"10.1016/j.msea.2025.148198","url":null,"abstract":"<div><div>The microstructure-dependent mechanism underlying the phenomenon of high tensile performance accompanied by serrated flow remains unclear in medium-manganese (medium-Mn) steel. This is primarily due to the conventional dynamic strain aging (DSA) theory, which focuses on the effect of carbon atoms while largely neglecting the influence of austenite characteristics. In this study, 0.06C-9Mn steel with varying austenite microstructures was fabricated through different rolling and annealing processes. The correlation between discontinuous and continuous mechanical behavior and austenite characteristics was investigated through microstructural characterization, local and global strain and kinetics measurements, and analytical modeling. To elucidate the microstructure-dependent discontinuous and continuous mechanical behavior of medium-Mn steel, two key parameters were introduced: the effective carbon content for pinning mobile dislocations (<em>X</em><sub>E</sub>) and the intensity coefficient of the TRIP effect (<em>T</em><sub>E</sub>), both of which were influenced by grain size and initial dislocation density under a given austenite volume fraction. An increase in grain size and initial dislocation density of austenite resulted in a decrease in <em>X</em><sub>E</sub> and an increase in <em>T</em><sub>E</sub>, with serrated flow emerging once the <em>X</em><sub>E</sub>-<em>T</em><sub>E</sub> balance reached a critical state. This phenomenon may be attributed to the activation of the DSA mechanism, where a weakened dislocation pinning ability is counteracted by enhanced dislocation mobility driven by the TRIP effect. Furthermore, an increase in <em>T</em><sub>E</sub> contributed to improved tensile performance in medium-Mn steel, leading to high tensile strength accompanied by serrated flow. Additionally, the discontinuous stepwise kinetics of strain-induced α′-martensite (SIM<sub>α′</sub>) transformation was accurately described using an analytical model based on strain surges or localization at the observation site as the PLC band propagated. These findings provide deeper insight into the mechanical behavior of medium-Mn steel and offer a pathway to achieving an optimized strength-elongation balance with minimized serrated flow.</div></div>","PeriodicalId":385,"journal":{"name":"Materials Science and Engineering: A","volume":"931 ","pages":"Article 148198"},"PeriodicalIF":6.1,"publicationDate":"2025-03-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143637127","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-03-17DOI: 10.1016/j.msea.2025.148221
Baishun Yang , Biao Li
Single-crystal turbine blades feature complex internal passages and surface cooling holes for forced convection air cooling, which introduce notches that may influence the blades' resistance to creep damage. This work studies the creep rupture behavior and notch effect of DD6 Ni-based single crystal superalloy through creep tests conducted in atmospheric air at 950 °C. Round bar specimens with varying notch features were examined, with stress concentration factors ranging from 1.0 to 5.0. The experimental results revealed a pronounced strengthening effect in the notched specimens, where creep rupture life was extended by 6–16 times compared to smoothed specimens, with the extension increasing as the stress concentration rose. A new creep damage model incorporated stress triaxiality factor was developed to predict the creep rupture life of the notched specimens, achieving a relative error within 20 % between simulation and experimental results. A competitive mechanism between maximum principal stress and stress triaxiality results in the creep notch strengthening effect, in which the stress facilitates the rupture but the stress triaxiality exerts an inhibition effect. As the stress concentration factor increases, the inhibition becomes increasingly dominant over the promotion and leads to longer creep rupture life.
单晶涡轮叶片具有复杂的内部通道和用于强制对流空气冷却的表面冷却孔，这些通道和冷却孔产生的缺口可能会影响叶片的抗蠕变损伤能力。本研究通过在 950 °C 大气中进行的蠕变试验，研究了 DD6 Ni 基单晶超合金的蠕变断裂行为和缺口效应。研究了具有不同缺口特征的圆棒试样，应力集中系数从 1.0 到 5.0 不等。实验结果表明，缺口试样具有明显的强化效果，与平滑试样相比，蠕变断裂寿命延长了 6 至 16 倍，随着应力集中度的增加，延长的时间也在增加。研究人员建立了一个包含应力三轴性因子的新蠕变损伤模型来预测缺口试样的蠕变断裂寿命，模拟结果与实验结果的相对误差在 20% 以内。最大主应力和应力三轴性之间的竞争机制导致了蠕变缺口强化效应，其中应力促进了断裂，而应力三轴性则起到了抑制作用。随着应力集中系数的增大，抑制作用会越来越明显地超过促进作用，从而导致蠕变断裂寿命的延长。
{"title":"Creep notch effect in DD6 Ni-based single crystal superalloy: Experimental and modeling studies","authors":"Baishun Yang , Biao Li","doi":"10.1016/j.msea.2025.148221","DOIUrl":"10.1016/j.msea.2025.148221","url":null,"abstract":"<div><div>Single-crystal turbine blades feature complex internal passages and surface cooling holes for forced convection air cooling, which introduce notches that may influence the blades' resistance to creep damage. This work studies the creep rupture behavior and notch effect of DD6 Ni-based single crystal superalloy through creep tests conducted in atmospheric air at 950 °C. Round bar specimens with varying notch features were examined, with stress concentration factors ranging from 1.0 to 5.0. The experimental results revealed a pronounced strengthening effect in the notched specimens, where creep rupture life was extended by 6–16 times compared to smoothed specimens, with the extension increasing as the stress concentration rose. A new creep damage model incorporated stress triaxiality factor was developed to predict the creep rupture life of the notched specimens, achieving a relative error within 20 % between simulation and experimental results. A competitive mechanism between maximum principal stress and stress triaxiality results in the creep notch strengthening effect, in which the stress facilitates the rupture but the stress triaxiality exerts an inhibition effect. As the stress concentration factor increases, the inhibition becomes increasingly dominant over the promotion and leads to longer creep rupture life.</div></div>","PeriodicalId":385,"journal":{"name":"Materials Science and Engineering: A","volume":"931 ","pages":"Article 148221"},"PeriodicalIF":6.1,"publicationDate":"2025-03-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143683495","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-03-17DOI: 10.1016/j.msea.2025.148217
Cong Liu , Fanli Kong , Hao Wang , Shengli Zhu , Guodong Liu , Akihisa Inoue
Zr-rich Zr70‒74Al7‒7.5Ni17‒20Cu2‒2.5 bulk metallic glasses (BMGs) with high yield strength (σy) of 1261–1316 MPa and large plastic strains of 8.4–11.3 % were formed in the as-cast state. The phase transition of these BMGs upon heating occurs through two stages of G → G + IQ → Zr2Ni + Zr5Al3 for the 70–72 %Zr alloys and three stages of G → G + β-Zr + ω-Zr → G + β-Zr + ω-Zr + Zr2Ni → α-Zr + Zr2Ni + Zr5Al3 for the 74 %Zr alloy. The partially transformed rods exhibit σy and plastic strain of 1318 MPa and 1.3 % for the 70 %Zr alloy and 1411 MPa and 3.9 % for the 74 %Zr alloy, respectively. It is noticed that the mixed phase alloys keep good plasticity and exhibit higher σy. These features are different from the previous results that the annealing-induced mixed phase alloys become always brittle and exhibit lower σy without plastic strain. The novel improvement of mechanical properties is due to the combination of homogeneous dispersion of β-Zr and ω-Zr phases with a size of 15–20 nm, good plasticity of β-Zr and ω-Zr phases, the existence of high density of faults in ω-Zr phase, and good plasticity of the residual glassy phase with Zr-rich compositions. The distinct increase in σy for the G + crystal composites is opposite to all the previous results where σy decreases significantly by the coexistence of crystalline phases. The present novel results are encouraging for future extension of application fields of BMGs.
{"title":"High mechanical strength and good plasticity of ZrAlNiCu bulk glassy alloys containing icosahedral or bcc β-Zr plus hexagonal ω-Zr phases prepared by annealing","authors":"Cong Liu , Fanli Kong , Hao Wang , Shengli Zhu , Guodong Liu , Akihisa Inoue","doi":"10.1016/j.msea.2025.148217","DOIUrl":"10.1016/j.msea.2025.148217","url":null,"abstract":"<div><div>Zr-rich Zr<sub>70‒74</sub>Al<sub>7‒7.5</sub>Ni<sub>17‒20</sub>Cu<sub>2‒2.5</sub> bulk metallic glasses (BMGs) with high yield strength (<em>σ</em><sub>y</sub>) of 1261–1316 MPa and large plastic strains of 8.4–11.3 % were formed in the as-cast state. The phase transition of these BMGs upon heating occurs through two stages of G → G + IQ → Zr<sub>2</sub>Ni + Zr<sub>5</sub>Al<sub>3</sub> for the 70–72 %Zr alloys and three stages of G → G + β-Zr + ω-Zr → G + β-Zr + ω-Zr + Zr<sub>2</sub>Ni → α-Zr + Zr<sub>2</sub>Ni + Zr<sub>5</sub>Al<sub>3</sub> for the 74 %Zr alloy. The partially transformed rods exhibit <em>σ</em><sub>y</sub> and plastic strain of 1318 MPa and 1.3 % for the 70 %Zr alloy and 1411 MPa and 3.9 % for the 74 %Zr alloy, respectively. It is noticed that the mixed phase alloys keep good plasticity and exhibit higher <em>σ</em><sub>y</sub>. These features are different from the previous results that the annealing-induced mixed phase alloys become always brittle and exhibit lower <em>σ</em><sub>y</sub> without plastic strain. The novel improvement of mechanical properties is due to the combination of homogeneous dispersion of β-Zr and ω-Zr phases with a size of 15–20 nm, good plasticity of β-Zr and ω-Zr phases, the existence of high density of faults in ω-Zr phase, and good plasticity of the residual glassy phase with Zr-rich compositions. The distinct increase in <em>σ</em><sub>y</sub> for the G + crystal composites is opposite to all the previous results where <em>σ</em><sub>y</sub> decreases significantly by the coexistence of crystalline phases. The present novel results are encouraging for future extension of application fields of BMGs.</div></div>","PeriodicalId":385,"journal":{"name":"Materials Science and Engineering: A","volume":"931 ","pages":"Article 148217"},"PeriodicalIF":6.1,"publicationDate":"2025-03-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143682997","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-03-17DOI: 10.1016/j.msea.2025.148226
Linda Squillaci , Magnus Neikter , Thomas Hansson , Robert Pederson , Johan Moverare
Powder bed fusion laser beam (PBF-LB) is one of the most widespread and highly researched additive manufacturing (AM) methods, spanning multiple industries. Its feedstock material is metallic powder, where a conventional particle size range is 15–50 μm. The present study focuses on Ti-6Al-4V powder with a wider particle size distribution (15–90 μm). Two process themes are evaluated: one minimising porosity and one maximising build rate through a fast laser scanning speed. The effect of two hot isostatic pressing (HIP) heat treatments on mechanical properties, one below and one above the β-transus, are compared to those of as-built and stress relieved material. Room temperature impact toughness and tensile testing are used to compare the materials by determining UTS and Yield strength, elongation and reduction of area for the different process conditions and post build heat treatments. The minimal porosity theme reaches properties comparable to conventional manufacturing processes at all heat treatment temperatures (i.e., UTS >860 MPa, 0.2 % Yield >795 MPa). The high productivity theme treated below β-transus provides further improvement in overall reduction of area (>45 %) and elongation (>20 %) with respect to the minimal porosity theme, by showing a bi-modal microstructure that is the result of a recrystallisation process. This phenomenon is triggered by the closure of lack of fusion (LoF) defects via hot isostatic pressing, due to a higher dislocation density at the tip of these particular defects. Impact energy for this condition increases whilst hardness and texture become less pronounced. It is demonstrated that in those cases where a fast scanning speed creates LoF defects, those can assist in modifying microstructure during the consolidation process which has a positive effect on ductility.
{"title":"Microstructure and mechanical properties of Ti-6Al-4V alloy fabricated using powder bed fusion – laser beam additive manufacturing process: Effect of hot isostatic pressing","authors":"Linda Squillaci , Magnus Neikter , Thomas Hansson , Robert Pederson , Johan Moverare","doi":"10.1016/j.msea.2025.148226","DOIUrl":"10.1016/j.msea.2025.148226","url":null,"abstract":"<div><div>Powder bed fusion laser beam (PBF-LB) is one of the most widespread and highly researched additive manufacturing (AM) methods, spanning multiple industries. Its feedstock material is metallic powder, where a conventional particle size range is 15–50 μm. The present study focuses on Ti-6Al-4V powder with a wider particle size distribution (15–90 μm). Two process themes are evaluated: one minimising porosity and one maximising build rate through a fast laser scanning speed. The effect of two hot isostatic pressing (HIP) heat treatments on mechanical properties, one below and one above the β-transus, are compared to those of as-built and stress relieved material. Room temperature impact toughness and tensile testing are used to compare the materials by determining UTS and Yield strength, elongation and reduction of area for the different process conditions and post build heat treatments. The minimal porosity theme reaches properties comparable to conventional manufacturing processes at all heat treatment temperatures (i.e., UTS >860 MPa, 0.2 % Yield >795 MPa). The high productivity theme treated below β-transus provides further improvement in overall reduction of area (>45 %) and elongation (>20 %) with respect to the minimal porosity theme, by showing a bi-modal microstructure that is the result of a recrystallisation process. This phenomenon is triggered by the closure of lack of fusion (LoF) defects via hot isostatic pressing, due to a higher dislocation density at the tip of these particular defects. Impact energy for this condition increases whilst hardness and texture become less pronounced. It is demonstrated that in those cases where a fast scanning speed creates LoF defects, those can assist in modifying microstructure during the consolidation process which has a positive effect on ductility.</div></div>","PeriodicalId":385,"journal":{"name":"Materials Science and Engineering: A","volume":"931 ","pages":"Article 148226"},"PeriodicalIF":6.1,"publicationDate":"2025-03-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143683097","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-03-17DOI: 10.1016/j.msea.2025.148219
Tao Wei, Alan Xu, Hanliang Zhu, Michael Drew, Tim Nicholls, Ondrej Muránsky
Understanding radiation damage resistance in Grade 91 steel (P91) is essential for the development of materials for future nuclear components. This study explores the combined effects of creep aging and helium ion irradiation on the microstructure and mechanical properties of P91 steel. Creep aging was conducted under a stress of 110 MPa at 625 °C for 475 h, followed by irradiation with 5 MeV helium ions to a fluence of 5.6 × 1017 ions/cm2, creating a uniform radiation-affected zone with an average damage level of 0.6 dpa. Microstructural changes and mechanical responses were assessed through detailed microstructural observations and nanoindentation, supported by finite element modelling. The results show that creep aging led to a slight reduction in hardness from 2.66 GPa to 2.45 GPa, primarily due to carbide coarsening. Significant irradiation hardening was observed, with hardness increasing by 87 % in the as-received condition and by 99 % in the creep-aged condition. A three-dimensional finite element model was developed to reverse-engineer stress-strain relationship from nanoindentation load-displacement data. This study underscores the significant impact of combined creep aging and irradiation on P91 steel, with important implications for its use in nuclear applications.
{"title":"Combined impact of creep aging and helium ion irradiation on P91 steel: Experiments and FE modelling","authors":"Tao Wei, Alan Xu, Hanliang Zhu, Michael Drew, Tim Nicholls, Ondrej Muránsky","doi":"10.1016/j.msea.2025.148219","DOIUrl":"10.1016/j.msea.2025.148219","url":null,"abstract":"<div><div>Understanding radiation damage resistance in Grade 91 steel (P91) is essential for the development of materials for future nuclear components. This study explores the combined effects of creep aging and helium ion irradiation on the microstructure and mechanical properties of P91 steel. Creep aging was conducted under a stress of 110 MPa at 625 °C for 475 h, followed by irradiation with 5 MeV helium ions to a fluence of 5.6 × 10<sup>17</sup> ions/cm<sup>2</sup>, creating a uniform radiation-affected zone with an average damage level of 0.6 dpa. Microstructural changes and mechanical responses were assessed through detailed microstructural observations and nanoindentation, supported by finite element modelling. The results show that creep aging led to a slight reduction in hardness from 2.66 GPa to 2.45 GPa, primarily due to carbide coarsening. Significant irradiation hardening was observed, with hardness increasing by 87 % in the as-received condition and by 99 % in the creep-aged condition. A three-dimensional finite element model was developed to reverse-engineer stress-strain relationship from nanoindentation load-displacement data. This study underscores the significant impact of combined creep aging and irradiation on P91 steel, with important implications for its use in nuclear applications.</div></div>","PeriodicalId":385,"journal":{"name":"Materials Science and Engineering: A","volume":"931 ","pages":"Article 148219"},"PeriodicalIF":6.1,"publicationDate":"2025-03-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143683493","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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