Pub Date : 2025-12-17DOI: 10.1016/j.actamat.2025.121843
Jianye He, Zezhou Li, Longkang Li, Jingchen Lin, Jun Wang, Shengxin Zhu, Fan Zhang, Lin Wang, Qinglei Zeng, Haosen Chen, Xingwang Cheng
The dynamic deformation, temperature evolution, and mechanical properties of NbTaTiV and NbTaTiVW alloys were investigated through high-speed photography, infrared temperature measurement, and the split Hopkinson pressure bar. The findings reveal that the adiabatic shear band initiated in the NbTaTiV and NbTaTiVW alloys when the temperature reaches approximately 160 ℃ and 115 ℃, respectively. It is evident that dependence exclusively on the thermal softening effect is inadequate to activate adiabatic shear bands. Instead, microstructural softening emerges as the predominant factor influencing their formation. We assessed the adiabatic shear sensitivity of NbTaTiV and NbTaTiVW alloys from distinct perspectives. It is noteworthy that the defect density observed in the NbTaTiV alloy is considerably greater than that found in the NbTaTiVW alloy. The deformation structure of the NbTaTiV alloy predominantly consists of dislocations, deformation twins, and kink bands, whereas the NbTaTiVW alloy is deformed by dislocations and deformation twins. The activation of multiple slip systems within the NbTaTiV alloy contributes to the delay of adiabatic shear failure. In addition, the participate phases in the NbTaTiVW alloy facilitate an increase in local dislocation density, thereby promoting adiabatic shear band failure. As a result, the energy dissipation of the adiabatic shear bands in the NbTaTiV alloy spans from 20.4 to 100.6 kJ/m², while the energy dissipation for the NbTaTiVW alloy is from 10.1 to 35.6 kJ/m². Our results and analyses contribute to formation mechanisms of shear band in refractory high-entropy alloys subjected to high strain rates.
{"title":"An in-situ study on the formation mechanism of adiabatic shear band in refractory high-entropy alloys","authors":"Jianye He, Zezhou Li, Longkang Li, Jingchen Lin, Jun Wang, Shengxin Zhu, Fan Zhang, Lin Wang, Qinglei Zeng, Haosen Chen, Xingwang Cheng","doi":"10.1016/j.actamat.2025.121843","DOIUrl":"https://doi.org/10.1016/j.actamat.2025.121843","url":null,"abstract":"The dynamic deformation, temperature evolution, and mechanical properties of NbTaTiV and NbTaTiVW alloys were investigated through high-speed photography, infrared temperature measurement, and the split Hopkinson pressure bar. The findings reveal that the adiabatic shear band initiated in the NbTaTiV and NbTaTiVW alloys when the temperature reaches approximately 160 ℃ and 115 ℃, respectively. It is evident that dependence exclusively on the thermal softening effect is inadequate to activate adiabatic shear bands. Instead, microstructural softening emerges as the predominant factor influencing their formation. We assessed the adiabatic shear sensitivity of NbTaTiV and NbTaTiVW alloys from distinct perspectives. It is noteworthy that the defect density observed in the NbTaTiV alloy is considerably greater than that found in the NbTaTiVW alloy. The deformation structure of the NbTaTiV alloy predominantly consists of dislocations, deformation twins, and kink bands, whereas the NbTaTiVW alloy is deformed by dislocations and deformation twins. The activation of multiple slip systems within the NbTaTiV alloy contributes to the delay of adiabatic shear failure. In addition, the participate phases in the NbTaTiVW alloy facilitate an increase in local dislocation density, thereby promoting adiabatic shear band failure. As a result, the energy dissipation of the adiabatic shear bands in the NbTaTiV alloy spans from 20.4 to 100.6 kJ/m², while the energy dissipation for the NbTaTiVW alloy is from 10.1 to 35.6 kJ/m². Our results and analyses contribute to formation mechanisms of shear band in refractory high-entropy alloys subjected to high strain rates.","PeriodicalId":238,"journal":{"name":"Acta Materialia","volume":"11 1","pages":""},"PeriodicalIF":9.4,"publicationDate":"2025-12-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145771374","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"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 : 2025-12-17DOI: 10.1016/j.actamat.2025.121834
Yiqi Guan , Zhixuan Zhang , Meifang Tang , Meiling He , Xiangyu Yan , Jianzhan Long , Qi Huang , Weibin Zhang , Yong Du , Alexander Hartmaier
The intrinsic trade-off between hardness and fracture toughness in carbide ceramics poses a severe challenge to their broader applications in advanced manufacturing. While grain refinement is known to enhance both properties, the underlying mechanisms through which microstructural factors (including grain size, grain orientation, and grain boundaries) govern crack propagation remain insufficiently understood. In this study, the fracture energy dissipation-based evaluation model within the phase-field framework was established to visualize fracture resistance in binderless WC cemented carbides. By integrating this model with experimental characterization, the influence of grain-scale microstructural factors on crack propagation was systematically investigated. The results reveal that the orientation-dependent fracture resistance of WC grains, grain boundary inclination, and especially grain size strongly influence the fracture mode and energy dissipation. Notably, grain refinement induces the increasement of transgranular fracture proportion, significantly increasing fracture energy dissipation. The binderless WC cemented carbide with finer grains (0.96 ± 0.01 μm) achieves a balanced combination of high fracture toughness (6.23 ± 0.16 ) and hardness (2231.19 ± 37.96 ). Both experimental and simulation results confirm that WC grain refinement is an effective strategy for improving fracture resistance, thereby validating the effectiveness of the fracture energy dissipation assessment model. The presently developed methodology provides critical insights into microstructure–crack interactions and opens new avenues for the microstructural design of high-toughness carbide ceramics.
{"title":"Fracture mode and toughening mechanism induced by microstructure in binderless WC cemented carbides: A phase-field simulation integrating energy dissipation analysis","authors":"Yiqi Guan , Zhixuan Zhang , Meifang Tang , Meiling He , Xiangyu Yan , Jianzhan Long , Qi Huang , Weibin Zhang , Yong Du , Alexander Hartmaier","doi":"10.1016/j.actamat.2025.121834","DOIUrl":"10.1016/j.actamat.2025.121834","url":null,"abstract":"<div><div>The intrinsic trade-off between hardness and fracture toughness in carbide ceramics poses a severe challenge to their broader applications in advanced manufacturing. While grain refinement is known to enhance both properties, the underlying mechanisms through which microstructural factors (including grain size, grain orientation, and grain boundaries) govern crack propagation remain insufficiently understood. In this study, the fracture energy dissipation-based evaluation model within the phase-field framework was established to visualize fracture resistance in binderless WC cemented carbides. By integrating this model with experimental characterization, the influence of grain-scale microstructural factors on crack propagation was systematically investigated. The results reveal that the orientation-dependent fracture resistance of WC grains, grain boundary inclination, and especially grain size strongly influence the fracture mode and energy dissipation. Notably, grain refinement induces the increasement of transgranular fracture proportion, significantly increasing fracture energy dissipation. The binderless WC cemented carbide with finer grains (0.96 ± 0.01 μm) achieves a balanced combination of high fracture toughness (6.23 ± 0.16 <span><math><mrow><mtext>MPa</mtext><mo>·</mo><msup><mrow><mrow><mi>m</mi></mrow></mrow><mrow><mn>1</mn><mo>/</mo><mn>2</mn></mrow></msup></mrow></math></span>) and hardness (2231.19 ± 37.96 <span><math><mtext>HV</mtext></math></span>). Both experimental and simulation results confirm that WC grain refinement is an effective strategy for improving fracture resistance, thereby validating the effectiveness of the fracture energy dissipation assessment model. The presently developed methodology provides critical insights into microstructure–crack interactions and opens new avenues for the microstructural design of high-toughness carbide ceramics.</div></div>","PeriodicalId":238,"journal":{"name":"Acta Materialia","volume":"305 ","pages":"Article 121834"},"PeriodicalIF":9.3,"publicationDate":"2025-12-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145771371","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"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 : 2025-12-16DOI: 10.1016/j.actamat.2025.121837
X.C. Cai , B.B. He , M.X. Huang
Ferritic steels with a nanograined structure are highly desirable for extreme applications in advanced nuclear reactors. Although nanograins can be readily generated through mechanical alloying, pronounced grain coarsening frequently occurs during the subsequent high-temperature sintering process, making it challenging to maintain the nanograined structure. The present work demonstrates that minor Zr alloying (0.8 wt.%, nominal) can effectively preserve the nanograined structure in typical ferritic oxide-dispersion-strengthened steels during high-temperature sintering via promoting homogeneous nanoprecipitation. To explore the role of Zr in influencing the precipitation of oxide nanoparticles (NPs), a series of multi-scale microstructural characterizations are performed. Contrary to the conventional view that Zr greatly accelerates the initial nucleation rate of NPs, this study reveals that Zr microalloying primarily operates by consuming excess oxygen during mechanical alloying, promptly eliminating the formation of competing oxides that are typically observed in steels without Zr. Consequently, Zr addition promotes the homogeneous precipitation of high-density Zr-Ti-O-rich NPs, which generate a strong dynamic pinning force that stabilizes the nanograins during high-temperature sintering, resulting in a nanograined ferritic steel with an average grain size of approximately 77 nm. This study highlights the often-overlooked issue of oxygen contamination control - an important consideration in the field of nanocrystalline metals and alloys fabricated by powder metallurgy and offers a cost-effective approach for designing high-performance nanostructured steels by precisely controlling the oxide NPs, which is supported by a deep understanding of the precipitation behaviors and their interactions with the nanostructure evolution.
具有纳米晶粒结构的铁素体钢在先进核反应堆的极端应用中是非常理想的。虽然通过机械合金化可以很容易地生成纳米晶粒，但在随后的高温烧结过程中，晶粒往往会出现明显的粗化，这给保持纳米晶粒结构带来了挑战。本研究表明，在高温烧结过程中，少量Zr合金（0.8 wt.%，标称）通过促进均匀的纳米沉淀，可以有效地保持典型铁素体氧化物分散强化钢的纳米晶粒结构。为了探索Zr对氧化纳米颗粒（NPs）析出的影响，进行了一系列多尺度的微观结构表征。与传统观点相反，Zr大大加快了NPs的初始形核速率，该研究表明，Zr微合金化主要是通过在机械合金化过程中消耗多余的氧气来实现的，迅速消除了在不含Zr的钢中通常观察到的竞争性氧化物的形成。因此，Zr的加入促进了高密度的富Zr- ti - o NPs的均匀析出，产生了强大的动态钉住力，在高温烧结过程中稳定了纳米晶粒，得到了平均晶粒尺寸约为77 nm的纳米铁素体钢。本研究强调了氧污染控制这一经常被忽视的问题——这是粉末冶金纳米晶金属和合金制造领域的一个重要考虑因素，并为通过精确控制氧化物NPs来设计高性能纳米结构钢提供了一种经济有效的方法，这得到了对沉淀行为及其与纳米结构演变相互作用的深入理解的支持。
{"title":"Preserving nanograined structure of ferritic steel during high-temperature sintering","authors":"X.C. Cai , B.B. He , M.X. Huang","doi":"10.1016/j.actamat.2025.121837","DOIUrl":"10.1016/j.actamat.2025.121837","url":null,"abstract":"<div><div>Ferritic steels with a nanograined structure are highly desirable for extreme applications in advanced nuclear reactors. Although nanograins can be readily generated through mechanical alloying, pronounced grain coarsening frequently occurs during the subsequent high-temperature sintering process, making it challenging to maintain the nanograined structure. The present work demonstrates that minor Zr alloying (0.8 wt.%, nominal) can effectively preserve the nanograined structure in typical ferritic oxide-dispersion-strengthened steels during high-temperature sintering via promoting homogeneous nanoprecipitation. To explore the role of Zr in influencing the precipitation of oxide nanoparticles (NPs), a series of multi-scale microstructural characterizations are performed. Contrary to the conventional view that Zr greatly accelerates the initial nucleation rate of NPs, this study reveals that Zr microalloying primarily operates by consuming excess oxygen during mechanical alloying, promptly eliminating the formation of competing oxides that are typically observed in steels without Zr. Consequently, Zr addition promotes the homogeneous precipitation of high-density Zr-Ti-O-rich NPs, which generate a strong dynamic pinning force that stabilizes the nanograins during high-temperature sintering, resulting in a nanograined ferritic steel with an average grain size of approximately 77 nm. This study highlights the often-overlooked issue of oxygen contamination control - an important consideration in the field of nanocrystalline metals and alloys fabricated by powder metallurgy and offers a cost-effective approach for designing high-performance nanostructured steels by precisely controlling the oxide NPs, which is supported by a deep understanding of the precipitation behaviors and their interactions with the nanostructure evolution.</div></div>","PeriodicalId":238,"journal":{"name":"Acta Materialia","volume":"305 ","pages":"Article 121837"},"PeriodicalIF":9.3,"publicationDate":"2025-12-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145760212","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"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 : 2025-12-16DOI: 10.1016/j.actamat.2025.121787
Theophilus Wallis , Reza Darvishi Kamachali
The density-based phase-field model for grain boundary (GB) thermodynamics and kinetics has offered a broad range of applications in alloy and microstructure design. Originally, this model is based on a potential energy terms that is connected to the cohesive energy of a given substance. A more rigorous approach, however, is a full consideration of an interatomic potential over the possible range of distance and therefore density. In Manuscript I of this series (Acta Materialia (2026) 121786), we developed and thoroughly analyzed the coarse-graining of atomistic GB structures. In this work (Manuscript II), we complete the coupling between atomic and mesoscale modeling of GBs by incorporating the full interatomic potentials into the density-based free energy functional. Using GB energies calculated from atomistic simulations, the coarse-graining approach and the atomistic-integrated density-based Gibbs free energy, we effectively evaluate the density gradient energy coefficient. We found that coupling the density-based model with atomistic potentials reveal physically-sound trends in the GB equilibrium properties. A universal equation was derived to describe the potential energy contribution to the GB energy and the gradient energy coefficient for BCC-Fe and -Mo GBs, similar to the universal equation for GB excess free volume presented in Manuscript I. The proposed approach provides a mesoscale density-based model rooted in atomic-scale characteristics for reliable predictions of GB properties.
基于密度的晶界热力学和动力学相场模型在合金和显微组织设计中有着广泛的应用。最初，该模型是基于与给定物质的内聚能相关的势能项。然而，更严格的方法是在可能的距离和密度范围内充分考虑原子间势。在本系列的手稿1 （Wallis and Darvishi Kamachali, 2025）中，我们发展并深入分析了原子GB结构的粗粒度。在本文中（手稿II），我们通过将完整的原子间电位纳入基于密度的自由能泛函中，完成了原子和中尺度模拟之间的耦合。利用原子模拟计算的GB能量、粗粒化方法和基于原子积分密度的吉布斯自由能，我们有效地评估了密度梯度能量系数。我们发现，将基于密度的模型与原子势耦合，揭示了GB平衡性质的物理合理趋势。导出了一个通用方程来描述BCC-Fe和-Mo GB的势能对GB能量和梯度能量系数的贡献，类似于手稿1中提出的GB过量自由体积的通用方程。该方法提供了一个基于原子尺度特征的基于中尺度密度的模型，用于可靠地预测GB性质。
{"title":"Linking atomistic and phase-field modeling of grain boundaries II: Incorporating atomistic potentials into free energy functional","authors":"Theophilus Wallis , Reza Darvishi Kamachali","doi":"10.1016/j.actamat.2025.121787","DOIUrl":"10.1016/j.actamat.2025.121787","url":null,"abstract":"<div><div>The density-based phase-field model for grain boundary (GB) thermodynamics and kinetics has offered a broad range of applications in alloy and microstructure design. Originally, this model is based on a potential energy terms that is connected to the cohesive energy of a given substance. A more rigorous approach, however, is a full consideration of an interatomic potential over the possible range of distance and therefore density. In Manuscript I of this series (Acta Materialia (2026) 121786), we developed and thoroughly analyzed the coarse-graining of atomistic GB structures. In this work (Manuscript II), we complete the coupling between atomic and mesoscale modeling of GBs by incorporating the full interatomic potentials into the density-based free energy functional. Using GB energies calculated from atomistic simulations, the coarse-graining approach and the atomistic-integrated density-based Gibbs free energy, we effectively evaluate the density gradient energy coefficient. We found that coupling the density-based model with atomistic potentials reveal physically-sound trends in the GB equilibrium properties. A universal equation was derived to describe the potential energy contribution to the GB energy and the gradient energy coefficient for BCC-Fe and -Mo GBs, similar to the universal equation for GB excess free volume presented in Manuscript I. The proposed approach provides a mesoscale density-based model rooted in atomic-scale characteristics for reliable predictions of GB properties.</div></div>","PeriodicalId":238,"journal":{"name":"Acta Materialia","volume":"305 ","pages":"Article 121787"},"PeriodicalIF":9.3,"publicationDate":"2025-12-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145760209","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"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 : 2025-12-16DOI: 10.1016/j.actamat.2025.121833
Yuheng Zhang , Yi Zhang , Yihuan Cao , Song Lu , Shuaicheng Zhu , Jiarui Zhu , Huadong Fu , Jianxin Xie
In this study, extensive formation of multi-type planar fault configurations and their intersections were found and examined at atomic resolution in a novel Co-Ni based wrought superalloy with exceptional creep resistance under 750 °C/620 MPa. In the initial creep strain, γ/γ′ interfacial shear arises from stacking fault (SF) propagation with characteristic widths of 5–10 nm. The steady-state creep regime reveals a coordinated deformation mechanism involving both γ′-penetrating microtwins and spatially confined V-shaped SFs within γ-channels. The SF interactions in the γ-channels not only nucleate stair-rod dislocations but also induce localized γ → HCP phase transformations. Concurrently, the sequential SF formation across adjacent {111} planes facilitates Burgers vector compensation through three leading partial dislocations, enabling formation of macroscopically zero-strain twins. Meanwhile, enhanced Co/Cr segregation along defect interfaces accelerates SF propagation while promoting cross-slip of leading partial dislocations, collectively enabling the development of high-density V-shaped fault architectures. Furthermore, the preferential segregation of W at SF-MT interfaces synergistically inhibits SF/MT propagation, while stabilizing the defect configuration, thereby improving the alloy’s creep resistance. The discovered deformation modalities enable mechanistic optimization of Co-Ni based superalloys through crystallographic defect engineering, establishing theoretical frameworks for microstructure-informed creep-resistant alloy design.
{"title":"Role of planar defects interactions within γ channels on creep resistance enhancement in a novel Co-Ni based superalloy","authors":"Yuheng Zhang , Yi Zhang , Yihuan Cao , Song Lu , Shuaicheng Zhu , Jiarui Zhu , Huadong Fu , Jianxin Xie","doi":"10.1016/j.actamat.2025.121833","DOIUrl":"10.1016/j.actamat.2025.121833","url":null,"abstract":"<div><div>In this study, extensive formation of multi-type planar fault configurations and their intersections were found and examined at atomic resolution in a novel Co-Ni based wrought superalloy with exceptional creep resistance under 750 °C/620 MPa. In the initial creep strain, γ/γ′ interfacial shear arises from stacking fault (SF) propagation with characteristic widths of 5–10 nm. The steady-state creep regime reveals a coordinated deformation mechanism involving both γ′-penetrating microtwins and spatially confined V-shaped SFs within γ-channels. The SF interactions in the γ-channels not only nucleate stair-rod dislocations but also induce localized γ → HCP phase transformations. Concurrently, the sequential SF formation across adjacent {111} planes facilitates Burgers vector compensation through three leading partial dislocations, enabling formation of macroscopically zero-strain twins. Meanwhile, enhanced Co/Cr segregation along defect interfaces accelerates SF propagation while promoting cross-slip of leading partial dislocations, collectively enabling the development of high-density V-shaped fault architectures. Furthermore, the preferential segregation of W at SF-MT interfaces synergistically inhibits SF/MT propagation, while stabilizing the defect configuration, thereby improving the alloy’s creep resistance. The discovered deformation modalities enable mechanistic optimization of Co-Ni based superalloys through crystallographic defect engineering, establishing theoretical frameworks for microstructure-informed creep-resistant alloy design.</div></div>","PeriodicalId":238,"journal":{"name":"Acta Materialia","volume":"305 ","pages":"Article 121833"},"PeriodicalIF":9.3,"publicationDate":"2025-12-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145760210","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The paper investigates the diffusion-induced grain boundary migration (DIGM) in six Fe-Cr-Ni ternary alloys exposed to steam at 480 °C. DIGM occurs due to the outward diffusion of Fe and Cr, essential for surface oxide formation, resulting in DIGM regions depleted in Fe and Cr and enriched in Ni. A significant finding is the tendency for preferential intergranular oxidation (PIO) to occur along these migrated grain boundaries, attributed to their enhanced element diffusivity. The extents of DIGM, PIO, and surface oxide thickness exhibited notable variations across the alloys with varying Ni contents, ranging from 11 wt.% to 75 wt.%. Further theoretical analysis and diffusion-barrier modeling were introduced to clarify the mechanistic role of Fe/Ni. The results reveal that Ni content modulates the competing diffusion behaviors of Fe, Cr, and Ni along grain boundaries, leading to a compositional transition from Fe-dominated to Ni-dominated diffusion regimes. The increasing Ni concentration reduces surface oxide thickness, thereby diminishing local diffusion and influencing the extent of both PIO and DIGM. However, due to the strong coupling among DIGM, PIO, and surface oxidation, their evolution with Ni content exhibits a complex, non-monotonic trend that is difficult to quantify precisely. This complexity arises from the interplay between oxidation-driven chemical potential gradients and composition-dependent grain boundary diffusivity. Generally, DIGM promotes PIO unless the outward and inward diffusivity of elements is significantly affected by surface oxides. However, in high corrosion-resistant alloys, DIGM inhibits the occurrence of PIO by facilitating the formation of an external protective chromia layer through enhanced Cr diffusion outwards.
{"title":"Insights into the complexities of diffusion-induced grain boundary migration in Fe-Cr-Ni ternary alloys","authors":"Kai Chen , Yuhao Zhou , Zhao Shen , Lefu Zhang , Fabio Scenini , Xiaoqin Zeng , Sergio Lozano-Perez","doi":"10.1016/j.actamat.2025.121836","DOIUrl":"10.1016/j.actamat.2025.121836","url":null,"abstract":"<div><div>The paper investigates the diffusion-induced grain boundary migration (DIGM) in six Fe-Cr-Ni ternary alloys exposed to steam at 480 °C. DIGM occurs due to the outward diffusion of Fe and Cr, essential for surface oxide formation, resulting in DIGM regions depleted in Fe and Cr and enriched in Ni. A significant finding is the tendency for preferential intergranular oxidation (PIO) to occur along these migrated grain boundaries, attributed to their enhanced element diffusivity. The extents of DIGM, PIO, and surface oxide thickness exhibited notable variations across the alloys with varying Ni contents, ranging from 11 wt.% to 75 wt.%. Further theoretical analysis and diffusion-barrier modeling were introduced to clarify the mechanistic role of Fe/Ni. The results reveal that Ni content modulates the competing diffusion behaviors of Fe, Cr, and Ni along grain boundaries, leading to a compositional transition from Fe-dominated to Ni-dominated diffusion regimes. The increasing Ni concentration reduces surface oxide thickness, thereby diminishing local diffusion and influencing the extent of both PIO and DIGM. However, due to the strong coupling among DIGM, PIO, and surface oxidation, their evolution with Ni content exhibits a complex, non-monotonic trend that is difficult to quantify precisely. This complexity arises from the interplay between oxidation-driven chemical potential gradients and composition-dependent grain boundary diffusivity. Generally, DIGM promotes PIO unless the outward and inward diffusivity of elements is significantly affected by surface oxides. However, in high corrosion-resistant alloys, DIGM inhibits the occurrence of PIO by facilitating the formation of an external protective chromia layer through enhanced Cr diffusion outwards.</div></div>","PeriodicalId":238,"journal":{"name":"Acta Materialia","volume":"305 ","pages":"Article 121836"},"PeriodicalIF":9.3,"publicationDate":"2025-12-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145760245","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"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 : 2025-12-16DOI: 10.1016/j.actamat.2025.121832
Zeng Liang, Kejiang Li, Jianliang Zhang, Alberto N. Conejo
Transitioning toward sustainable steel production requires replacing carbon-intensive processes with hydrogen-based direct reduction (HyDR) of iron oxides. However, the atomic-level mechanism by which metallic iron nucleates and crystallizes during reduction remains elusive. Here, Deep Potential Molecular Dynamics (DeepMD) simulations, trained on a comprehensive density functional theory dataset, are employed to explore the amorphous-to-crystalline transformation of iron during hydrogen-driven reduction of wüstite. The resulting potential achieves DFT-level accuracy (MAE ≈ 14.4 meV/atom, 0.277 eV/Å) while enabling nanosecond-scale simulations of thousands of atoms. Free-energy calculations reveal that BCC α-Fe is the most stable phase between 773 and 1173 K, driving spontaneous ordering observed in molecular dynamics trajectories. Complementary NEB analyses quantify orientation-dependent nucleation barriers, showing that Fe adsorption and transition states are most favorable on FeO(110) and Fe-terminated FeO(111) surfaces, consistent with their rapid crystallization in simulations. Interfacial analyses demonstrate strong orientation- and termination-dependent adhesion, with FeO(111)/α-Fe(110) and Fe-terminated surfaces most effectively promoting BCC nucleation. The combined thermodynamic, kinetic, and interfacial insights provide a unified atomic-scale picture of iron formation, offering guidance for the rational design of efficient, low-carbon HyDR processes.
{"title":"Atomic-scale mechanism of iron crystallization during hydrogen reduction revealed by an accurate deep-learning force field","authors":"Zeng Liang, Kejiang Li, Jianliang Zhang, Alberto N. Conejo","doi":"10.1016/j.actamat.2025.121832","DOIUrl":"10.1016/j.actamat.2025.121832","url":null,"abstract":"<div><div>Transitioning toward sustainable steel production requires replacing carbon-intensive processes with hydrogen-based direct reduction (HyDR) of iron oxides. However, the atomic-level mechanism by which metallic iron nucleates and crystallizes during reduction remains elusive. Here, Deep Potential Molecular Dynamics (DeepMD) simulations, trained on a comprehensive density functional theory dataset, are employed to explore the amorphous-to-crystalline transformation of iron during hydrogen-driven reduction of wüstite. The resulting potential achieves DFT-level accuracy (MAE ≈ 14.4 meV/atom, 0.277 eV/Å) while enabling nanosecond-scale simulations of thousands of atoms. Free-energy calculations reveal that BCC α-Fe is the most stable phase between 773 and 1173 K, driving spontaneous ordering observed in molecular dynamics trajectories. Complementary NEB analyses quantify orientation-dependent nucleation barriers, showing that Fe adsorption and transition states are most favorable on FeO(110) and Fe-terminated FeO(111) surfaces, consistent with their rapid crystallization in simulations. Interfacial analyses demonstrate strong orientation- and termination-dependent adhesion, with FeO(111)/α-Fe(110) and Fe-terminated surfaces most effectively promoting BCC nucleation. The combined thermodynamic, kinetic, and interfacial insights provide a unified atomic-scale picture of iron formation, offering guidance for the rational design of efficient, low-carbon HyDR processes.</div></div>","PeriodicalId":238,"journal":{"name":"Acta Materialia","volume":"305 ","pages":"Article 121832"},"PeriodicalIF":9.3,"publicationDate":"2025-12-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145771376","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"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 : 2025-12-15DOI: 10.1016/j.actamat.2025.121831
Ahmad Mirzaei, Shen J. Dillon
Arrhenius kinetics are central to high-temperature creep but have not routinely produced quantitative, parameter-sparse descriptions of low-temperature plasticity, stress–strain response, or Hall–Petch scaling. We introduce Arrhenius analogues of the Taylor hardening and Hall–Petch models that incorporate two essential microstructural descriptors: a local stress concentration factor and the volume fraction of rate-limiting interaction sites . When combined with a minimal dislocation-density evolution law, this “Arrhenius mechanics” framework fits Hall–Petch datasets, true stress–strain curves, and the strain-rate and temperature dependence of strength across materials and microstructures. The formulation also reproduces inverse Hall–Petch behavior and strain softening without ad hoc assumptions. Fitted activation parameters are physically plausible, with and . Expressing grain boundary-dislocation interactions and dislocation-segment depinning within a common Arrhenius form yields a compact set of scaling relations in stress, grain size, and dislocation spacing that support (i) cross-experiment parameter transfer (e.g., from nanopillar tests to polycrystalline yield), (ii) extrapolation across strain rates and temperatures, and (iii) construction of deformation-mechanism maps using a small number of measurable quantities. The formulation derives from a convex dissipation potential, ensuring thermodynamic consistency. The results suggest accounting for and is sufficient to unify plasticity and creep descriptions within a single Arrhenius framework.
{"title":"An Arrhenius mechanics model for polycrystalline plasticity and creep","authors":"Ahmad Mirzaei, Shen J. Dillon","doi":"10.1016/j.actamat.2025.121831","DOIUrl":"10.1016/j.actamat.2025.121831","url":null,"abstract":"<div><div>Arrhenius kinetics are central to high-temperature creep but have not routinely produced quantitative, parameter-sparse descriptions of low-temperature plasticity, stress–strain response, or Hall–Petch scaling. We introduce Arrhenius analogues of the Taylor hardening and Hall–Petch models that incorporate two essential microstructural descriptors: a local stress concentration factor <span><math><mi>ϕ</mi></math></span> and the volume fraction of rate-limiting interaction sites <span><math><mstyle><mi>Ξ</mi></mstyle></math></span>. When combined with a minimal dislocation-density evolution law, this “Arrhenius mechanics” framework fits Hall–Petch datasets, true stress–strain curves, and the strain-rate and temperature dependence of strength across materials and microstructures. The formulation also reproduces inverse Hall–Petch behavior and strain softening without ad hoc assumptions. Fitted activation parameters are physically plausible, with <span><math><mrow><msup><mrow><mi>H</mi></mrow><mo>*</mo></msup><mo>∼</mo><mn>0.1</mn><mo>−</mo><mn>5</mn><mspace></mspace><mi>e</mi><mi>V</mi></mrow></math></span> and <span><math><mrow><msup><mrow><mi>v</mi></mrow><mo>*</mo></msup><mo>∼</mo><mn>0.1</mn><mo>−</mo><mn>10</mn><mspace></mspace><msup><mrow><mi>b</mi></mrow><mn>3</mn></msup></mrow></math></span>. Expressing grain boundary-dislocation interactions and dislocation-segment depinning within a common Arrhenius form yields a compact set of scaling relations in stress, grain size, and dislocation spacing that support (i) cross-experiment parameter transfer (e.g., from nanopillar tests to polycrystalline yield), (ii) extrapolation across strain rates and temperatures, and (iii) construction of deformation-mechanism maps using a small number of measurable quantities<strong>.</strong> The formulation derives from a convex dissipation potential, ensuring thermodynamic consistency. The results suggest accounting for <span><math><mi>ϕ</mi></math></span> and <span><math><mstyle><mi>Ξ</mi></mstyle></math></span> is sufficient to unify plasticity and creep descriptions within a single Arrhenius framework.</div></div>","PeriodicalId":238,"journal":{"name":"Acta Materialia","volume":"305 ","pages":"Article 121831"},"PeriodicalIF":9.3,"publicationDate":"2025-12-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145753322","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The longstanding gap between atomistic and mesoscale simulations partly lies in the absence of a direct, physically grounded connection between atomic structure and mesoscale fields. In this work, we present a robust coarse-graining approach to systematically investigate the connection between phase-field and atomistic simulations of grain boundaries (GBs). The atomistic structures of 408 GBs in BCC-Fe and -Mo were studies to compute and analyze a continuous atomic density field. We discover a fundamental relationship between the GB density — defined as the average atomic density at the GB plane — and the GB excess free volume, an integral property of the boundary. An almost perfect linear correlation between the GB atomic density and GB excess free volume is identified. We also show that the width of BCC GBs, when scaled by the lattice constant, approaches a universal constant value. The relationships among GB density, width, and energy are systematically examined for various GB planes, and the GB energy–density correlations are classified with respect to GB types. It turns out that the atomic planes forming the GB strongly influence both the GB density and excess volume. The current results establish a dependable framework to bridge across scales, enabling density-based phase-field modeling of GBs with atomistic fidelity and enhancing the predictive reliability of mesoscale simulations.
{"title":"Linking atomistic and phase-field modeling of grain boundaries I: Coarse-graining atomistic structures","authors":"Theophilus Wallis , Sutatch Ratanaphan , Reza Darvishi Kamachali","doi":"10.1016/j.actamat.2025.121786","DOIUrl":"10.1016/j.actamat.2025.121786","url":null,"abstract":"<div><div>The longstanding gap between atomistic and mesoscale simulations partly lies in the absence of a direct, physically grounded connection between atomic structure and mesoscale fields. In this work, we present a robust coarse-graining approach to systematically investigate the connection between phase-field and atomistic simulations of grain boundaries (GBs). The atomistic structures of 408 GBs in BCC-Fe and -Mo were studies to compute and analyze a continuous atomic density field. We discover a fundamental relationship between the GB density — defined as the average atomic density at the GB plane — and the GB excess free volume, an integral property of the boundary. An almost perfect linear correlation between the GB atomic density and GB excess free volume is identified. We also show that the width of BCC GBs, when scaled by the lattice constant, approaches a universal constant value. The relationships among GB density, width, and energy are systematically examined for various GB planes, and the GB energy–density correlations are classified with respect to GB types. It turns out that the atomic planes forming the GB strongly influence both the GB density and excess volume. The current results establish a dependable framework to bridge across scales, enabling density-based phase-field modeling of GBs with atomistic fidelity and enhancing the predictive reliability of mesoscale simulations.</div></div>","PeriodicalId":238,"journal":{"name":"Acta Materialia","volume":"305 ","pages":"Article 121786"},"PeriodicalIF":9.3,"publicationDate":"2025-12-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145753286","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"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 : 2025-12-15DOI: 10.1016/j.actamat.2025.121829
Ting Liu , Yunzhu Shi , Liuliu Han , Fei Zhang , Wei Chen , Hongyuan Wan , Chao Ma , Alexander Schökel , Yan Ma , Shaolou Wei , Claudio Pistidda , Zhifeng Lei , Zhaoping Lu
In metals and alloys, solute segregation at grain boundaries typically undermines cohesion and ductility. Here, we overturn this paradigm by showing that solvent Fe atoms can preferentially enrich low-angle grain boundaries (LAGBs) in a ferrous alloy, dramatically enhancing ductility. Cold rolling and aging generate coherent nanoprecipitates, a high dislocation density, and abundant LAGBs in an austenitic matrix, yielding an ultrahigh tensile yield strength of ∼ 1.74 GPa. Moreover, the solvent Fe enrichment at LAGBs lowers local stacking fault energy and activates austenite-to-martensite transformation under load. This transformation-induced plasticity effect stabilizes plastic flow, enabling a uniform elongation of ∼ 26.2 % despite the alloy’s exceptional strength. Our findings challenge conventional views of segregation and offer a new design strategy for ultra-strong, highly ductile alloys.
{"title":"Solvent-enriched interface enables ductility in an ultrastrong alloy","authors":"Ting Liu , Yunzhu Shi , Liuliu Han , Fei Zhang , Wei Chen , Hongyuan Wan , Chao Ma , Alexander Schökel , Yan Ma , Shaolou Wei , Claudio Pistidda , Zhifeng Lei , Zhaoping Lu","doi":"10.1016/j.actamat.2025.121829","DOIUrl":"10.1016/j.actamat.2025.121829","url":null,"abstract":"<div><div>In metals and alloys, solute segregation at grain boundaries typically undermines cohesion and ductility. Here, we overturn this paradigm by showing that solvent Fe atoms can preferentially enrich low-angle grain boundaries (LAGBs) in a ferrous alloy, dramatically enhancing ductility. Cold rolling and aging generate coherent nanoprecipitates, a high dislocation density, and abundant LAGBs in an austenitic matrix, yielding an ultrahigh tensile yield strength of ∼ 1.74 GPa. Moreover, the solvent Fe enrichment at LAGBs lowers local stacking fault energy and activates austenite-to-martensite transformation under load. This transformation-induced plasticity effect stabilizes plastic flow, enabling a uniform elongation of ∼ 26.2 % despite the alloy’s exceptional strength. Our findings challenge conventional views of segregation and offer a new design strategy for ultra-strong, highly ductile alloys.</div></div>","PeriodicalId":238,"journal":{"name":"Acta Materialia","volume":"305 ","pages":"Article 121829"},"PeriodicalIF":9.3,"publicationDate":"2025-12-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145753278","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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