Pub Date : 2025-04-04DOI: 10.1016/j.actamat.2025.120987
Maximilian A. Wollenweber , Jonas Werner , Carl F. Kusche , Chunhua Tian , Pei-Ling Sun , Jannik Gerlach , Talal Al-Samman , Sandra Korte-Kerzel
Forming-induced damage strongly influences the service life and mechanical properties of components made from 16MnCrS5 steel. This damage is initiated in the vicinity of MnS inclusions, which fracture or delaminate at their interfaces due to the mechanical contrast to the steel matrix. Forming processes are often conducted at elevated temperatures; however, the plasticity of MnS at these temperatures in correlation with crystallographic orientation have not been fully explored. In this study, we aim to uncover the high-temperature properties of MnS using micropillar compression and TEM analysis. We then relate them to damage prevalence observed in steel at elevated temperatures with high resolution SEM imaging in combination with AI-assisted damage analysis. We demonstrate that the mechanical contrast of MnS and steel influences the damage prevalence significantly showing a minimum at 400 °C. We additionally determine the CRSS for the primary slip system in the temperature range from 20 °C to 600 °C and the CRSS for the secondary slip system at temperatures of 400 °C and 600 °C. We show that MnS exhibits a yield strength anomaly at 400 °C in specific orientations and at slow loading rates that is accompanied by a change of the active slip system. We relate this yield strength anomaly to thermally activated cross-slip and increased impurity mobility at elevated temperatures.
{"title":"On the plasticity of MnS at elevated temperatures and its influence on damage prevalence","authors":"Maximilian A. Wollenweber , Jonas Werner , Carl F. Kusche , Chunhua Tian , Pei-Ling Sun , Jannik Gerlach , Talal Al-Samman , Sandra Korte-Kerzel","doi":"10.1016/j.actamat.2025.120987","DOIUrl":"10.1016/j.actamat.2025.120987","url":null,"abstract":"<div><div>Forming-induced damage strongly influences the service life and mechanical properties of components made from 16MnCrS5 steel. This damage is initiated in the vicinity of MnS inclusions, which fracture or delaminate at their interfaces due to the mechanical contrast to the steel matrix. Forming processes are often conducted at elevated temperatures; however, the plasticity of MnS at these temperatures in correlation with crystallographic orientation have not been fully explored. In this study, we aim to uncover the high-temperature properties of MnS using micropillar compression and TEM analysis. We then relate them to damage prevalence observed in steel at elevated temperatures with high resolution SEM imaging in combination with AI-assisted damage analysis. We demonstrate that the mechanical contrast of MnS and steel influences the damage prevalence significantly showing a minimum at 400<!--> <!-->°C. We additionally determine the CRSS for the primary <span><math><mrow><mo>{</mo><mn>1</mn><mspace></mspace><mn>1</mn><mspace></mspace><mn>0</mn><mo>}</mo></mrow></math></span> <span><math><mrow><mo>〈</mo><mn>1</mn><mspace></mspace><mover><mrow><mn>1</mn></mrow><mo>¯</mo></mover><mspace></mspace><mn>0</mn><mo>〉</mo></mrow></math></span> slip system in the temperature range from 20<!--> <!-->°C to 600<!--> <!-->°C and the CRSS for the secondary <span><math><mrow><mo>{</mo><mn>1</mn><mspace></mspace><mn>1</mn><mspace></mspace><mn>1</mn><mo>}</mo></mrow></math></span> <span><math><mrow><mo>〈</mo><mn>1</mn><mspace></mspace><mover><mrow><mn>1</mn></mrow><mo>¯</mo></mover><mspace></mspace><mn>0</mn><mo>〉</mo></mrow></math></span> slip system at temperatures of 400<!--> <!-->°C and 600<!--> <!-->°C. We show that MnS exhibits a yield strength anomaly at 400<!--> <!-->°C in specific orientations and at slow loading rates that is accompanied by a change of the active slip system. We relate this yield strength anomaly to thermally activated cross-slip and increased impurity mobility at elevated temperatures.</div></div>","PeriodicalId":238,"journal":{"name":"Acta Materialia","volume":"291 ","pages":"Article 120987"},"PeriodicalIF":8.3,"publicationDate":"2025-04-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143782787","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 : 2025-04-04DOI: 10.1016/j.actamat.2025.121004
Jiawen Zhang , Xufei Fang , Wenjun Lu
Dislocations in ceramics at room temperature are attracting increasing research interest. Dislocations may bring a new perspective for tuning physical and mechanical properties in advanced ceramics. Here, we investigate the dislocation density dependent micromechanical properties of single-crystal SrTiO3 by tuning the dislocation densities (from ∼1010 m-2 up to ∼1014 m-2). Using micropillar compression tests, we find the samples exhibit a transition from brittle fracture (if no dislocation is present in the pillars) to plastic yield (with pre-engineered dislocations in the pillars). Within the regime of plastic deformation, the yield strength and plastic flow behavior exhibit a strong dependence on the dislocation density. The yield strength first decreases and then increases with the increase of dislocation densities. Detailed examination via post-mortem transmission electron microscopy reveals a complex evolution of the dislocation structure, highlighting the critical role played by dislocations in regulating the brittle/ductile behavior in SrTiO3 at room temperature. Our findings shed new light on dislocation-mediated mechanical properties in ceramics and may provide designing guidelines for the prospective dislocation-based devices.
{"title":"Impact of dislocation densities on the microscale strength of single-crystal strontium titanate","authors":"Jiawen Zhang , Xufei Fang , Wenjun Lu","doi":"10.1016/j.actamat.2025.121004","DOIUrl":"10.1016/j.actamat.2025.121004","url":null,"abstract":"<div><div>Dislocations in ceramics at room temperature are attracting increasing research interest. Dislocations may bring a new perspective for tuning physical and mechanical properties in advanced ceramics. Here, we investigate the dislocation density dependent micromechanical properties of single-crystal SrTiO<sub>3</sub> by tuning the dislocation densities (from ∼10<sup>10</sup> m<sup>-2</sup> up to ∼10<sup>14</sup> m<sup>-2</sup>). Using micropillar compression tests, we find the samples exhibit a transition from brittle fracture (if no dislocation is present in the pillars) to plastic yield (with pre-engineered dislocations in the pillars). Within the regime of plastic deformation, the yield strength and plastic flow behavior exhibit a strong dependence on the dislocation density. The yield strength first decreases and then increases with the increase of dislocation densities. Detailed examination via post-mortem transmission electron microscopy reveals a complex evolution of the dislocation structure, highlighting the critical role played by dislocations in regulating the brittle/ductile behavior in SrTiO<sub>3</sub> at room temperature. Our findings shed new light on dislocation-mediated mechanical properties in ceramics and may provide designing guidelines for the prospective dislocation-based devices.</div></div>","PeriodicalId":238,"journal":{"name":"Acta Materialia","volume":"291 ","pages":"Article 121004"},"PeriodicalIF":8.3,"publicationDate":"2025-04-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143768388","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
An Er410 NiMo martensitic stainless steel thin wall was built using wire-arc additive manufacturing (WAAM) based on cold metal transfer (CMT) to study the microstructural evolution during elaboration. For this purpose, thermal cycles were recorded in situ using thermocouples inserted in the melt pool and building parameters were tailored to maximize the reproducibility of thermal cycles. The wall structure was characterized from the macroscopic to the atomic scale and its hardness as well as its tensile properties were measured. Three macroscopic zones could be differentiated in the wall depending on the thermal conditions: the top zone, fully re-austenitized during deposition of the last layer, the middle zone, tempered by at least one thermal cycle and the bottom zone, under thermal influence of the substrate. The microstructure of the wall is almost fully martensitic, organized inside large columnar grains oriented towards the building direction, with a small fraction of residual inter-lath austenite only detected in the tempered middle layers. At the microscopic and mesoscopic scales, C, Cr and Ni atomic segregations are revealed in the top zone, and C and Cr segregations in the middle zone. During re-austenitization, necklaces of new small prior austenite grains (PAGs) formed at the boundaries of the previous ones. A strong microstructural differentiation occurs during the 3rd reheating, where the top of a layer is fully re-austenitized while the middle and bottom parts experience an inter-critical and subcritical thermal treatment, respectively. This differentiation leads to periodic oscillations of the materials’ hardness in the middle zone along the building direction which are mainly explained by different degrees of tempering in the martensite. Mechanisms are proposed to explain the different microstructural evolutions during elaboration. Finally, tensile testing shows isotropic mechanical properties, which are close to those of the desired commercial “tempered” state.
{"title":"Multiscale characterization of WAAMed martensitic stainless steel: Correlation between experimental AM thermal cycles, microstructural evolution and mechanical properties","authors":"Jules L’Hostis , Ludovic Thuinet , Emmanuel Cadel , Marie-Noëlle Avettand-Fènoël","doi":"10.1016/j.actamat.2025.120972","DOIUrl":"10.1016/j.actamat.2025.120972","url":null,"abstract":"<div><div>An Er410 NiMo martensitic stainless steel thin wall was built using wire-arc additive manufacturing (WAAM) based on cold metal transfer (CMT) to study the microstructural evolution during elaboration. For this purpose, thermal cycles were recorded <em>in situ</em> using thermocouples inserted in the melt pool and building parameters were tailored to maximize the reproducibility of thermal cycles. The wall structure was characterized from the macroscopic to the atomic scale and its hardness as well as its tensile properties were measured. Three macroscopic zones could be differentiated in the wall depending on the thermal conditions: the top zone, fully re-austenitized during deposition of the last layer, the middle zone, tempered by at least one thermal cycle and the bottom zone, under thermal influence of the substrate. The microstructure of the wall is almost fully martensitic, organized inside large columnar grains oriented towards the building direction, with a small fraction of residual inter-lath austenite only detected in the tempered middle layers. At the microscopic and mesoscopic scales, C, Cr and Ni atomic segregations are revealed in the top zone, and C and Cr segregations in the middle zone. During re-austenitization, necklaces of new small prior austenite grains (PAGs) formed at the boundaries of the previous ones. A strong microstructural differentiation occurs during the 3rd reheating, where the top of a layer is fully re-austenitized while the middle and bottom parts experience an inter-critical and subcritical thermal treatment, respectively. This differentiation leads to periodic oscillations of the materials’ hardness in the middle zone along the building direction which are mainly explained by different degrees of tempering in the martensite. Mechanisms are proposed to explain the different microstructural evolutions during elaboration. Finally, tensile testing shows isotropic mechanical properties, which are close to those of the desired commercial “tempered” state.</div></div>","PeriodicalId":238,"journal":{"name":"Acta Materialia","volume":"291 ","pages":"Article 120972"},"PeriodicalIF":8.3,"publicationDate":"2025-04-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143800509","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"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 : 2025-04-02DOI: 10.1016/j.actamat.2025.121008
Eunwook Jeong , Sang-Geul Lee , Seung Min Yu , Jeongeun Chae , Seung Zeon Han , Gun-Hwan Lee , Yoshifumi Ikoma , Eun-Ae Choi , Jungheum Yun
Electronic and optoelectronic devices usually include metal electrodes, particularly Au, Ag, and Cu layers, owing to their excellent conductivities. Achieving robust adhesion between these coinage metal electrode layers and various oxide substrates remains a considerable challenge due to the weak O affinities of coinage metals, specifically that of Au. Direct contact between the electrodes and substrates without electronically deficient intermediates, such as Ti and Cr adhesive layers, is highly desirable for improving device performance. In this study, we numerically hypothesize and experimentally confirm that the incorporation of excess atomic O interstitials into the Au/oxide interfaces and Au surfaces substantially enhances the direct adhesion between the Au electrodes and oxide substrates, while preserving the uniqueness of the Au electrodes. Our findings highlight the role of O interstitials as chemical bridges between Au electrodes and oxide substrates in film structures. The unprecedented direct adhesion of the Au electrodes to oxide substrates was detected (exhibiting enhanced adhesion strength from 0.02 to > 50 N); this adhesion strength is substantially higher than those (< 20 N) afforded by conventional techniques. The proposed strategy was extended to Cu and Ag electrodes with compelling evidence using atomic N and O interstitials. The superstrong adhesion of these metal film electrodes was realized without compromising the metal electrode integrity, paving the way for advancing the integration of metal electrodes into devices.
电子和光电设备通常包括金属电极，尤其是金层、银层和铜层，因为它们具有出色的导电性。由于共价金属（尤其是金）的 O 亲和力较弱，要在这些共价金属电极层和各种氧化物基底之间实现牢固的粘附仍然是一个相当大的挑战。为了提高器件性能，电极与基底直接接触而不使用电子缺陷中间体（如钛和铬粘合层）是非常理想的。在本研究中，我们通过数值假设和实验证实，在金/氧化物界面和金表面掺入过量的原子 O 间隙可大大增强金电极与氧化物基底之间的直接粘附性，同时保持金电极的独特性。我们的研究结果凸显了 O 间隙在薄膜结构中作为金电极和氧化物基底之间化学桥梁的作用。我们检测到了金电极与氧化物基底前所未有的直接粘附力（粘附力从 0.02 到 50 N 不等）；这种粘附力大大高于传统技术（20 N）。利用原子 N 和 O 间质，我们将所提出的策略扩展到了铜和银电极，并获得了令人信服的证据。这些金属膜电极的超强附着力是在不损害金属电极完整性的情况下实现的，为推动金属电极集成到设备中铺平了道路。
{"title":"Superstrong direct adhesion of Au, Ag, and Cu electrodes to oxide substrates via interfacial engineering","authors":"Eunwook Jeong , Sang-Geul Lee , Seung Min Yu , Jeongeun Chae , Seung Zeon Han , Gun-Hwan Lee , Yoshifumi Ikoma , Eun-Ae Choi , Jungheum Yun","doi":"10.1016/j.actamat.2025.121008","DOIUrl":"10.1016/j.actamat.2025.121008","url":null,"abstract":"<div><div>Electronic and optoelectronic devices usually include metal electrodes, particularly Au, Ag, and Cu layers, owing to their excellent conductivities. Achieving robust adhesion between these coinage metal electrode layers and various oxide substrates remains a considerable challenge due to the weak O affinities of coinage metals, specifically that of Au. Direct contact between the electrodes and substrates without electronically deficient intermediates, such as Ti and Cr adhesive layers, is highly desirable for improving device performance. In this study, we numerically hypothesize and experimentally confirm that the incorporation of excess atomic O interstitials into the Au/oxide interfaces and Au surfaces substantially enhances the direct adhesion between the Au electrodes and oxide substrates, while preserving the uniqueness of the Au electrodes. Our findings highlight the role of O interstitials as chemical bridges between Au electrodes and oxide substrates in film structures. The unprecedented direct adhesion of the Au electrodes to oxide substrates was detected (exhibiting enhanced adhesion strength from 0.02 to > 50 N); this adhesion strength is substantially higher than those (< 20 N) afforded by conventional techniques. The proposed strategy was extended to Cu and Ag electrodes with compelling evidence using atomic N and O interstitials. The superstrong adhesion of these metal film electrodes was realized without compromising the metal electrode integrity, paving the way for advancing the integration of metal electrodes into devices.</div></div>","PeriodicalId":238,"journal":{"name":"Acta Materialia","volume":"291 ","pages":"Article 121008"},"PeriodicalIF":8.3,"publicationDate":"2025-04-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143766599","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 : 2025-04-02DOI: 10.1016/j.actamat.2025.120970
You Sub Kim , Taeuk Kang , Soon-Ku Hong , Jamieson Brechtl , Mikhail Lebyodkin , Yi-Hsuan Cheng , E-Wen Huang , Peter K. Liaw , Stefanus Harjo , Wu Gong , Ching-Yu Chiang , Soo Yeol Lee
Metallic materials are known to exhibit low-temperature discontinuous deformation (i.e., low-temperature serrated deformation, LTSD) at cryogenic temperatures, which can lead to sudden failures or catastrophic accidents. Therefore, understanding LTSD is crucial for ensuring material stability and reliability in a cryogenic environment. Thus far, the widely accepted explanations for the origins of LTSD can be categorized into two mechanisms: (i) dislocation-based mechanical instability and (ii) thermomechanical instability. However, interpreting LTSD using each theory independently has limitations in clearly elucidating the LTSD mechanism. Therefore, the current understanding of LTSD remains insufficient and is still subject to debate because it is challenging to prove experimentally. To address this issue, we suggest a novel LTSD mechanism, namely a thermally induced dislocation dynamics model, based on the experimental evidence that considers both the dislocation dynamics and thermomechanical characteristics at cryogenic temperatures. Furthermore, we present a modified deformation-mechanism map of a SS316L that incorporates the newly proposed LTSD mechanisms. The origin of LTSD is considered in the unique framework of dislocation behavior under severely limited thermal-vibration energy at cryogenic temperatures, leading to the dislocation avalanches and development of hierarchical dislocation networks, including multiple lattice defects. Therewith, the localized heating generated from dislocation avalanches induces multiple types of LTSD and gives rise to transitions from the heterogeneous to homogeneous deformation. Our findings highlight the rate-dependent nature of LTSD and negative strain-rate sensitivity in the strength-elongation relationship and include the first observation of changes in small stress fluctuations and their relationship to the changes in larger serrations.
{"title":"Fundamental mechanisms of discontinuous deformation in metals for cryogenic-environment applications","authors":"You Sub Kim , Taeuk Kang , Soon-Ku Hong , Jamieson Brechtl , Mikhail Lebyodkin , Yi-Hsuan Cheng , E-Wen Huang , Peter K. Liaw , Stefanus Harjo , Wu Gong , Ching-Yu Chiang , Soo Yeol Lee","doi":"10.1016/j.actamat.2025.120970","DOIUrl":"10.1016/j.actamat.2025.120970","url":null,"abstract":"<div><div>Metallic materials are known to exhibit low-temperature discontinuous deformation (i.e., low-temperature serrated deformation, LTSD) at cryogenic temperatures, which can lead to sudden failures or catastrophic accidents. Therefore, understanding LTSD is crucial for ensuring material stability and reliability in a cryogenic environment. Thus far, the widely accepted explanations for the origins of LTSD can be categorized into two mechanisms: (i) dislocation-based mechanical instability and (ii) thermomechanical instability. However, interpreting LTSD using each theory independently has limitations in clearly elucidating the LTSD mechanism. Therefore, the current understanding of LTSD remains insufficient and is still subject to debate because it is challenging to prove experimentally. To address this issue, we suggest a novel LTSD mechanism, namely a thermally induced dislocation dynamics model, based on the experimental evidence that considers both the dislocation dynamics and thermomechanical characteristics at cryogenic temperatures. Furthermore, we present a modified deformation-mechanism map of a SS316L that incorporates the newly proposed LTSD mechanisms. The origin of LTSD is considered in the unique framework of dislocation behavior under severely limited thermal-vibration energy at cryogenic temperatures, leading to the dislocation avalanches and development of hierarchical dislocation networks, including multiple lattice defects. Therewith, the localized heating generated from dislocation avalanches induces multiple types of LTSD and gives rise to transitions from the heterogeneous to homogeneous deformation. Our findings highlight the rate-dependent nature of LTSD and negative strain-rate sensitivity in the strength-elongation relationship and include the first observation of changes in small stress fluctuations and their relationship to the changes in larger serrations.</div></div>","PeriodicalId":238,"journal":{"name":"Acta Materialia","volume":"292 ","pages":"Article 120970"},"PeriodicalIF":8.3,"publicationDate":"2025-04-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143839229","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 : 2025-04-01DOI: 10.1016/j.actamat.2025.120966
A. Morawiec
The geometric state of a flat boundary is frequently described using the so-called macroscopic parameters. They are a principal tool for dealing with interfaces at the continuous scale. The paper describes a new method for macroscopic identification of boundaries. The proposed approach is based on Euler angles representing orientations of the crystals. Two pairs of the angles are directly related to two vectors normal to the boundary plane in the crystal reference frames, and the new boundary representation can be viewed as a triplet composed of these vectors and the angle of rotation about the axis perpendicular to the plane. The representation resembles the ‘interface-plane scheme’, but unlike the latter, it is a proper parameterization. Basic practical aspects of the parameterization (such as equivalences due to symmetries, fundamental regions, uniform distribution of boundaries) are considered. The parameterization is applied to examination of Bulatov-Reed-Kumar model of grain boundary energy and reveals its previously unknown features. The proposed boundary identification method, apart from its use in numerical calculations, appeals to physical intuition.
{"title":"Interface-plane parameterization for macroscopic grain boundary identification","authors":"A. Morawiec","doi":"10.1016/j.actamat.2025.120966","DOIUrl":"10.1016/j.actamat.2025.120966","url":null,"abstract":"<div><div>The geometric state of a flat boundary is frequently described using the so-called macroscopic parameters. They are a principal tool for dealing with interfaces at the continuous scale. The paper describes a new method for macroscopic identification of boundaries. The proposed approach is based on Euler angles representing orientations of the crystals. Two pairs of the angles are directly related to two vectors normal to the boundary plane in the crystal reference frames, and the new boundary representation can be viewed as a triplet composed of these vectors and the angle of rotation about the axis perpendicular to the plane. The representation resembles the ‘interface-plane scheme’, but unlike the latter, it is a proper parameterization. Basic practical aspects of the parameterization (such as equivalences due to symmetries, fundamental regions, uniform distribution of boundaries) are considered. The parameterization is applied to examination of Bulatov-Reed-Kumar model of grain boundary energy and reveals its previously unknown features. The proposed boundary identification method, apart from its use in numerical calculations, appeals to physical intuition.</div></div>","PeriodicalId":238,"journal":{"name":"Acta Materialia","volume":"291 ","pages":"Article 120966"},"PeriodicalIF":8.3,"publicationDate":"2025-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143745649","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 : 2025-04-01DOI: 10.1016/j.actamat.2025.120968
I.S. Winter , T. Frolov
We introduce a grain boundary (GB) translation vector, , to describe and quantify the domain of the microscopic degrees of freedom of GBs. It has long been recognized that for fixed macroscopic degrees of freedom of a GB there exists a large multiplicity of states characterized by different relative grain translations. More recently another degree of freedom, , the number of GB atoms, has emerged and is now recognized as an equally important component of GB structural multiplicity. In this work, we show that all GB microstates can be uniquely characterized by their value of , which is located within the Wigner–Seitz (WS) cell of the Displacement-Shift-Complete lattice (DSCL) of the GB. The GB translation vector captures information about both the translation state and the number of GB atoms. We show that the density of GB microstates inside the WS cell of the DSCL is not uniform and can form clusters that correspond to different GB phases. The vectors connecting the centers of the clusters correspond to the Burgers vectors of GB phase junctions, which can be predicted without building the junctions. Using , we quantify GB excess shear and argue that it is defined up to a DSCL vector, which has implications for thermodynamic equilibrium conditions. Additionally, this work generalizes the definition of the number of GB atoms to asymmetric boundaries.
{"title":"Quantifying and visualizing the microscopic degrees of freedom of grain boundaries in the Wigner–Seitz cell of the displacement-shift-complete lattice","authors":"I.S. Winter , T. Frolov","doi":"10.1016/j.actamat.2025.120968","DOIUrl":"10.1016/j.actamat.2025.120968","url":null,"abstract":"<div><div>We introduce a grain boundary (GB) translation vector, <span><math><msup><mrow><mi>t</mi></mrow><mrow><mi>W</mi><mi>S</mi></mrow></msup></math></span>, to describe and quantify the domain of the microscopic degrees of freedom of GBs. It has long been recognized that for fixed macroscopic degrees of freedom of a GB there exists a large multiplicity of states characterized by different relative grain translations. More recently another degree of freedom, <span><math><mrow><mo>[</mo><mi>n</mi><mo>]</mo></mrow></math></span>, the number of GB atoms, has emerged and is now recognized as an equally important component of GB structural multiplicity. In this work, we show that all GB microstates can be uniquely characterized by their value of <span><math><msup><mrow><mi>t</mi></mrow><mrow><mi>W</mi><mi>S</mi></mrow></msup></math></span>, which is located within the Wigner–Seitz (WS) cell of the Displacement-Shift-Complete lattice (DSCL) of the GB. The GB translation vector captures information about both the translation state and the number of GB atoms. We show that the density of GB microstates inside the WS cell of the DSCL is not uniform and can form clusters that correspond to different GB phases. The vectors connecting the centers of the clusters correspond to the Burgers vectors of GB phase junctions, which can be predicted without building the junctions. Using <span><math><msup><mrow><mi>t</mi></mrow><mrow><mi>W</mi><mi>S</mi></mrow></msup></math></span>, we quantify GB excess shear and argue that it is defined up to a DSCL vector, which has implications for thermodynamic equilibrium conditions. Additionally, this work generalizes the definition of the number of GB atoms <span><math><mrow><mo>[</mo><mi>n</mi><mo>]</mo></mrow></math></span> to asymmetric boundaries.</div></div>","PeriodicalId":238,"journal":{"name":"Acta Materialia","volume":"291 ","pages":"Article 120968"},"PeriodicalIF":8.3,"publicationDate":"2025-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143790950","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 : 2025-04-01DOI: 10.1016/j.actamat.2025.121007
Boyang Gu , Yang Li , Adrian Diaz , Yipeng Peng , David L. McDowell , Youping Chen
This work presents a multiscale study of the uniaxial compression of Si pillars, with diameters ranging from 50 nm to 360 nm, using the Concurrent Atomistic-Continuum (CAC) method. The simulations reproduce the brittle and ductile deformation behaviors of Si pillars observed in experiments. For defect-free Si pillars compressed by a perfectly smooth flat punch with a repulsive force field to reflect an assumed rigid indenter, dislocations are nucleated from the corner of the bottom surface for pillars with diameters of 100 nm and below, while for pillars with diameters of 220 nm and above, dislocations nucleate from the top surface; multiple slip systems are activated in all pillars except for the pillar with a diameter of 50 nm. A strong size effect is thus demonstrated with regard to the nucleation of dislocations. Another key finding is the critical role of defects on the indenter surface. For a perfectly flat indenter, all the defect-free Si pillars with diameters ranging from 50 nm to 360 nm exhibit ductile deformation. By contrast, for an indenter with surface steps, all pillars with diameters of 100 nm and above deform in a brittle manner. These surface steps cause sequential nucleation of dislocations and activation of two slip systems, leading to dislocation intersection and formation of a sessile Lomer lock. Continued pileups of dislocations against the Lomer lock lead to the initiation of a crack at the intersection. The deformation mechanism underlying the crack formation is thus demonstrated.
{"title":"Brittle and Ductile Deformations in Uniaxial Compression of Si Micropillars","authors":"Boyang Gu , Yang Li , Adrian Diaz , Yipeng Peng , David L. McDowell , Youping Chen","doi":"10.1016/j.actamat.2025.121007","DOIUrl":"10.1016/j.actamat.2025.121007","url":null,"abstract":"<div><div>This work presents a multiscale study of the uniaxial compression of Si pillars, with diameters ranging from 50 nm to 360 nm, using the Concurrent Atomistic-Continuum (CAC) method. The simulations reproduce the brittle and ductile deformation behaviors of Si pillars observed in experiments. For defect-free Si pillars compressed by a perfectly smooth flat punch with a repulsive force field to reflect an assumed rigid indenter, dislocations are nucleated from the corner of the bottom surface for pillars with diameters of 100 nm and below, while for pillars with diameters of 220 nm and above, dislocations nucleate from the top surface; multiple slip systems are activated in all pillars except for the pillar with a diameter of 50 nm. A strong size effect is thus demonstrated with regard to the nucleation of dislocations. Another key finding is the critical role of defects on the indenter surface. For a perfectly flat indenter, all the defect-free Si pillars with diameters ranging from 50 nm to 360 nm exhibit ductile deformation. By contrast, for an indenter with surface steps, all pillars with diameters of 100 nm and above deform in a brittle manner. These surface steps cause sequential nucleation of dislocations and activation of two slip systems, leading to dislocation intersection and formation of a sessile Lomer lock. Continued pileups of dislocations against the Lomer lock lead to the initiation of a crack at the intersection. The deformation mechanism underlying the crack formation is thus demonstrated.</div></div>","PeriodicalId":238,"journal":{"name":"Acta Materialia","volume":"291 ","pages":"Article 121007"},"PeriodicalIF":8.3,"publicationDate":"2025-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143800528","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 : 2025-04-01DOI: 10.1016/j.actamat.2025.121005
Hongyao Zhang , Haotian Gao , Tianxiang Jiang , Qiang Feng , Huili Liu , Tongsuo Lu , Beibei Xu , Wujie Qiu , He Lin , Kunpeng Zhao
Understanding and engineering thermal transport in complex structures is essential for the development of materials with ultralow lattice thermal conductivity. In this study, we examine the unusual thermal transport behavior of Mg2Sn-based high-entropy materials, using a combination of pair distribution function (PDF) analysis, first-principles calculations, and theoretical modeling. Our findings demonstrate that the crystalline high-entropy materials exhibit glass-like thermal transports, characterized by an exceptionally low lattice thermal conductivity that increases monotonically with increasing temperature across the entire measured range, devoid of the characteristic peaks typical of crystalline materials. This unique behavior is attributed to the large atomic displacement parameter (ADP) of Mg atoms, which causes the Einstein oscillators to significantly reduce lattice thermal conductivity, complemented by the strong scattering of phonons by the nanoscale chemical fluctuations and a dense concentration of point defects within the high-entropy structure. These insights deepen our understanding of thermal transport in complex-structured materials, such as Mg2Sn-related compounds, and offer a foundation for designing new materials with tailored thermal conductivities for advanced thermal management and thermoelectric applications.
{"title":"Glass-like thermal conduction in crystalline Mg2Sn-based high-entropy materials","authors":"Hongyao Zhang , Haotian Gao , Tianxiang Jiang , Qiang Feng , Huili Liu , Tongsuo Lu , Beibei Xu , Wujie Qiu , He Lin , Kunpeng Zhao","doi":"10.1016/j.actamat.2025.121005","DOIUrl":"10.1016/j.actamat.2025.121005","url":null,"abstract":"<div><div>Understanding and engineering thermal transport in complex structures is essential for the development of materials with ultralow lattice thermal conductivity. In this study, we examine the unusual thermal transport behavior of Mg<sub>2</sub>Sn-based high-entropy materials, using a combination of pair distribution function (PDF) analysis, first-principles calculations, and theoretical modeling. Our findings demonstrate that the crystalline high-entropy materials exhibit glass-like thermal transports, characterized by an exceptionally low lattice thermal conductivity that increases monotonically with increasing temperature across the entire measured range, devoid of the characteristic peaks typical of crystalline materials. This unique behavior is attributed to the large atomic displacement parameter (ADP) of Mg atoms, which causes the Einstein oscillators to significantly reduce lattice thermal conductivity, complemented by the strong scattering of phonons by the nanoscale chemical fluctuations and a dense concentration of point defects within the high-entropy structure. These insights deepen our understanding of thermal transport in complex-structured materials, such as Mg<sub>2</sub>Sn-related compounds, and offer a foundation for designing new materials with tailored thermal conductivities for advanced thermal management and thermoelectric applications.</div></div>","PeriodicalId":238,"journal":{"name":"Acta Materialia","volume":"291 ","pages":"Article 121005"},"PeriodicalIF":8.3,"publicationDate":"2025-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143790997","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 : 2025-04-01DOI: 10.1016/j.actamat.2025.120982
So Yeon Kim , Ju Li
Rechargeable all-solid-state batteries (ASSBs) offer improved safety and the potential for advanced chemistries, but the susceptibility of solid electrolytes (SEs) to electrochemo-mechanical degradation remains a major challenge. This degradation manifests in two modes: a fast longitudinal mode, such as short-circuiting dendrites, and a slow transverse mode, such as in-plane cracking and isolated alkali metal formation. While prior research has mainly focused on mitigating the longitudinal mode, the transverse mode is becoming increasingly critical, particularly under the practically required pressure-less conditions. Here, we demonstrate through thermodynamic modeling that multilayering the SE separator can mitigate electrochemical instabilities attributed to abrupt jumps in the chemical potential of neutral Li atoms (Li) within the SE separator, contributing to transverse mechanical degradation. We first derive an analytic solution for the Li chemical potential profile within SEs, confirming its extreme sensitivity to SE-specific redox-sensitive electronic conductivities and boundary potentials at the SE edges. Inspired by this sensitivity, we propose and theoretically demonstrate that multilayering can confine potential jumps to less detrimental spatial/Li-potential regimes, thereby mitigating transverse degradation and delaying longitudinal degradation as well. We then discuss the effects of both extrinsic and intrinsic factors on this approach, along with their practical implications. Overall, our findings suggest that multilayered SEs can provide a comprehensive strategy against both transverse and longitudinal degradation modes, outlining critical parameters to consider in the development of pressure-less ASSBs with enhanced electrochemical performance and damage resistance.
{"title":"Electrochemical potential in multilayer solid electrolytes and mechanical implications","authors":"So Yeon Kim , Ju Li","doi":"10.1016/j.actamat.2025.120982","DOIUrl":"10.1016/j.actamat.2025.120982","url":null,"abstract":"<div><div>Rechargeable all-solid-state batteries (ASSBs) offer improved safety and the potential for advanced chemistries, but the susceptibility of solid electrolytes (SEs) to electrochemo-mechanical degradation remains a major challenge. This degradation manifests in two modes: a fast longitudinal mode, such as short-circuiting dendrites, and a slow transverse mode, such as in-plane cracking and isolated alkali metal formation. While prior research has mainly focused on mitigating the longitudinal mode, the transverse mode is becoming increasingly critical, particularly under the practically required pressure-less conditions. Here, we demonstrate through thermodynamic modeling that multilayering the SE separator can mitigate electrochemical instabilities attributed to abrupt jumps in the chemical potential of neutral Li atoms (Li<span><math><msup><mrow></mrow><mrow><mn>0</mn></mrow></msup></math></span>) within the SE separator, contributing to transverse mechanical degradation. We first derive an analytic solution for the Li<span><math><msup><mrow></mrow><mrow><mn>0</mn></mrow></msup></math></span> chemical potential profile within SEs, confirming its extreme sensitivity to SE-specific redox-sensitive electronic conductivities and boundary potentials at the SE edges. Inspired by this sensitivity, we propose and theoretically demonstrate that multilayering can confine potential jumps to less detrimental spatial/Li<span><math><msup><mrow></mrow><mrow><mn>0</mn></mrow></msup></math></span>-potential regimes, thereby mitigating transverse degradation and delaying longitudinal degradation as well. We then discuss the effects of both extrinsic and intrinsic factors on this approach, along with their practical implications. Overall, our findings suggest that multilayered SEs can provide a comprehensive strategy against both transverse and longitudinal degradation modes, outlining critical parameters to consider in the development of pressure-less ASSBs with enhanced electrochemical performance and damage resistance.</div></div>","PeriodicalId":238,"journal":{"name":"Acta Materialia","volume":"291 ","pages":"Article 120982"},"PeriodicalIF":8.3,"publicationDate":"2025-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143807346","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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