Pub Date : 2025-03-11DOI: 10.1016/j.actamat.2025.120933
Xiong Zhang , Haoling Luo , Xiaoliang Cao , Guang Han , Hong Wu , Yu Zhang , Bin Zhang , Guoyu Wang , Xiaoyuan Zhou
n-Type Mg3Sb2-based materials have attracted considerable attention as high-performance thermoelectrics. However, the dimensionless figure of merit (zT) of its p-type counterparts remains much lower, limiting its practical applications. Herein, a remarkable increase in the power factor of p-type Mg3Sb2 is realized by incorporating 50 % YbZn2Sb2, which is related to the effectively decreased crystal field splitting energy and increased carrier concentration and mobility. Through entropy engineering, the lattice thermal conductivity at 323 K of Cd-alloyed (Mg3.1Sb2)0.5(YbZn2Sb2)0.5 is decreased by 56 % and 23 % as compared to that of Mg3.1Sb2 and (Mg3.1Sb2)0.5(YbZn2Sb2)0.5, respectively. Further, the hole concentration is optimized by Ag doping, resulting in a high power factor of 1.03 mW m−1 K−2 at 773 K. Eventually, a maximum zT value of ∼1.34 at 773 K and an average zT of ∼0.77 between 323 K and 773 K are achieved in (Mg3.07Ag0.03Sb2)0.5(YbZn1.2Cd0.8Sb2)0.5, which are excellent zT values for p-type Mg3Sb2-based materials. The present study offers an effective strategy for designing high-performance p-type Mg3Sb2-based thermoelectric materials.
{"title":"Achieving excellent thermoelectric performance in p-type Mg3Sb2-based Zintl materials via synergistic band engineering and entropy engineering","authors":"Xiong Zhang , Haoling Luo , Xiaoliang Cao , Guang Han , Hong Wu , Yu Zhang , Bin Zhang , Guoyu Wang , Xiaoyuan Zhou","doi":"10.1016/j.actamat.2025.120933","DOIUrl":"10.1016/j.actamat.2025.120933","url":null,"abstract":"<div><div>n-Type Mg<sub>3</sub>Sb<sub>2</sub>-based materials have attracted considerable attention as high-performance thermoelectrics. However, the dimensionless figure of merit (<em>zT</em>) of its p-type counterparts remains much lower, limiting its practical applications. Herein, a remarkable increase in the power factor of p-type Mg<sub>3</sub>Sb<sub>2</sub> is realized by incorporating 50 % YbZn<sub>2</sub>Sb<sub>2</sub>, which is related to the effectively decreased crystal field splitting energy and increased carrier concentration and mobility. Through entropy engineering, the lattice thermal conductivity at 323 K of Cd-alloyed (Mg<sub>3.1</sub>Sb<sub>2</sub>)<sub>0.5</sub>(YbZn<sub>2</sub>Sb<sub>2</sub>)<sub>0.5</sub> is decreased by 56 % and 23 % as compared to that of Mg<sub>3.1</sub>Sb<sub>2</sub> and (Mg<sub>3.1</sub>Sb<sub>2</sub>)<sub>0.5</sub>(YbZn<sub>2</sub>Sb<sub>2</sub>)<sub>0.5</sub>, respectively. Further, the hole concentration is optimized by Ag doping, resulting in a high power factor of 1.03 mW m<sup>−1</sup> K<sup>−2</sup> at 773 K. Eventually, a maximum <em>zT</em> value of ∼1.34 at 773 K and an average <em>zT</em> of ∼0.77 between 323 K and 773 K are achieved in (Mg<sub>3.07</sub>Ag<sub>0.03</sub>Sb<sub>2</sub>)<sub>0.5</sub>(YbZn<sub>1.2</sub>Cd<sub>0.8</sub>Sb<sub>2</sub>)<sub>0.5</sub>, which are excellent <em>zT</em> values for p-type Mg<sub>3</sub>Sb<sub>2</sub>-based materials. The present study offers an effective strategy for designing high-performance p-type Mg<sub>3</sub>Sb<sub>2</sub>-based thermoelectric materials.</div></div>","PeriodicalId":238,"journal":{"name":"Acta Materialia","volume":"289 ","pages":"Article 120933"},"PeriodicalIF":8.3,"publicationDate":"2025-03-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143599157","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 : 2025-03-11DOI: 10.1016/j.actamat.2025.120925
Heng Kang , Huanrong Liu , Qingan Li , Nannan Ren , Yunjiang Wang , Pengfei Guan
Establishing a quantitative structure-property relationship is essential for the development and design of new materials. However, this approach faces significant challenges in amorphous materials, where even a quantitative description of atomic structure is nearly impossible. In this study, we examined the packing characteristics of atoms based on their contributions to excess low-frequency vibrational modes in a model metallic glass. Our investigation spans more than eight orders of magnitude in effective cooling rates, ensuring the exploration of a broader range of thermal history states and their associated properties. We found that atoms with smaller contributions tend to cluster spatially, while those with larger contributions form branched, quasi-two-dimensional structures with fractal characteristics. As a result, the critical fraction of atoms required to form a percolated network is significantly lower for high-contribution atoms than for low-contribution ones. In both types of networks, the correlation between connectivity and contribution follows an exponential relationship, with higher sensitivity in networks composed of large-contribution atoms. As the system's energy decreases, the intensity of the low-frequency excess peak diminishes, yet the critical fraction of atoms remains constant, irrespective of whether the networks are composed of high- or low-contribution atoms. This reveals a hidden topological invariance in the atomic packing features of metallic glasses.
{"title":"Invariant topological feature of atomic packing in a model metallic glass","authors":"Heng Kang , Huanrong Liu , Qingan Li , Nannan Ren , Yunjiang Wang , Pengfei Guan","doi":"10.1016/j.actamat.2025.120925","DOIUrl":"10.1016/j.actamat.2025.120925","url":null,"abstract":"<div><div>Establishing a quantitative structure-property relationship is essential for the development and design of new materials. However, this approach faces significant challenges in amorphous materials, where even a quantitative description of atomic structure is nearly impossible. In this study, we examined the packing characteristics of atoms based on their contributions to excess low-frequency vibrational modes in a model metallic glass. Our investigation spans more than eight orders of magnitude in effective cooling rates, ensuring the exploration of a broader range of thermal history states and their associated properties. We found that atoms with smaller contributions tend to cluster spatially, while those with larger contributions form branched, quasi-two-dimensional structures with fractal characteristics. As a result, the critical fraction of atoms required to form a percolated network is significantly lower for high-contribution atoms than for low-contribution ones. In both types of networks, the correlation between connectivity and contribution follows an exponential relationship, with higher sensitivity in networks composed of large-contribution atoms. As the system's energy decreases, the intensity of the low-frequency excess peak diminishes, yet the critical fraction of atoms remains constant, irrespective of whether the networks are composed of high- or low-contribution atoms. This reveals a hidden topological invariance in the atomic packing features of metallic glasses.</div></div>","PeriodicalId":238,"journal":{"name":"Acta Materialia","volume":"289 ","pages":"Article 120925"},"PeriodicalIF":8.3,"publicationDate":"2025-03-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143599635","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 : 2025-03-11DOI: 10.1016/j.actamat.2025.120929
Qingmei Gong , Haihong Jiang , Martin Peterlechner , Sergiy V. Divinski , Gerhard Wilde
Ge2Sb2Te5 is the most commonly used material for phase change random access memory. In this work, a chemically homogeneous 200 nm thick layer of amorphous Ge2Sb2Te5 was grown on a single crystal Si wafer using DC magnetron sputtering and applying a stoichiometric target at room temperature. A metastable NaCl-type structure having a face-centered-cubic lattice was obtained by subsequent annealing at 473 K for 30 min. The crystal structure and microstructure were analyzed by X-ray diffraction and transmission electron microscopy. Te self-diffusion was measured by secondary ion mass spectroscopy applying a highly enriched natural 122Te isotope. The Te self-diffusion coefficients follow an Arrhenius law in the temperature range between room temperature and 353 K with an activation enthalpy of (125.0 ± 5) kJ/mol. The diffusion data are discussed in terms of either grain boundary diffusion contributions or, alternatively, in relation to volume diffusion enhanced by structural vacancies. In comparison to the amorphous counterpart, the Te self-diffusion rates in crystalline Ge2Sb2Te5 are only marginally lower and exceed the volume diffusivities of Te in crystalline Te by more than four orders of magnitude, indicating that the structural vacancies seem to determine the measured diffusion rates.
{"title":"Tellurium self-diffusion in crystalline Ge2Sb2Te5 phase change material","authors":"Qingmei Gong , Haihong Jiang , Martin Peterlechner , Sergiy V. Divinski , Gerhard Wilde","doi":"10.1016/j.actamat.2025.120929","DOIUrl":"10.1016/j.actamat.2025.120929","url":null,"abstract":"<div><div>Ge<sub>2</sub>Sb<sub>2</sub>Te<sub>5</sub> is the most commonly used material for phase change random access memory. In this work, a chemically homogeneous 200 nm thick layer of amorphous Ge<sub>2</sub>Sb<sub>2</sub>Te<sub>5</sub> was grown on a single crystal Si wafer using DC magnetron sputtering and applying a stoichiometric target at room temperature. A metastable NaCl-type structure having a face-centered-cubic lattice was obtained by subsequent annealing at 473 K for 30 min. The crystal structure and microstructure were analyzed by X-ray diffraction and transmission electron microscopy. Te self-diffusion was measured by secondary ion mass spectroscopy applying a highly enriched natural <sup>122</sup>Te isotope. The Te self-diffusion coefficients follow an Arrhenius law in the temperature range between room temperature and 353 K with an activation enthalpy of (125.0 ± 5) kJ/mol. The diffusion data are discussed in terms of either grain boundary diffusion contributions or, alternatively, in relation to volume diffusion enhanced by structural vacancies. In comparison to the amorphous counterpart, the Te self-diffusion rates in crystalline Ge<sub>2</sub>Sb<sub>2</sub>Te<sub>5</sub> are only marginally lower and exceed the volume diffusivities of Te in crystalline Te by more than four orders of magnitude, indicating that the structural vacancies seem to determine the measured diffusion rates.</div></div>","PeriodicalId":238,"journal":{"name":"Acta Materialia","volume":"289 ","pages":"Article 120929"},"PeriodicalIF":8.3,"publicationDate":"2025-03-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143682923","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 : 2025-03-11DOI: 10.1016/j.actamat.2025.120930
Hongchao Li , Jun Wang , Jiawang Zhao , Jinshan Li , M.W. Fu
Metallic materials exhibiting ultrahigh strength coupled with exceptional ductility play a pivotal role in advanced industries, yet enhancing strength typically sacrifices strain hardening and ductility. This study presents a strategy that activated an innovative deformation mechanism to overcome the long-standing trade-off between strength and ductility in an L12-strengthened Al5Ti8(FeCoNi)86.9B0.1 high-entropy alloy. After aging at 765 °C for 4 hours, the alloy achieved a yield strength of 1227 MPa, an ultimate tensile strength of 1742 MPa, and an elongation of 39.9%, attributed to the ultrahigh and sustained strain hardening induced by phase transformation within dynamically refined microbands during deformation. Our findings indicated that FCC→BCC transformation within the microbands was more favorable in an FCC matrix with a larger width. Furthermore, a high density of superlattice intrinsic stacking faults and Lomer-Cottrell locks in L12 phase were formed, leading to additional strain hardening of the alloy. The synergistic interaction between phase transformation and microband formation offers a promising approach for designing novel high-performance alloys with exceptional strength and ductility.
{"title":"Phase transformation within dynamically refined microbands inducing ultrahigh and sustained strain hardening in high-entropy alloys containing L12 precipitates","authors":"Hongchao Li , Jun Wang , Jiawang Zhao , Jinshan Li , M.W. Fu","doi":"10.1016/j.actamat.2025.120930","DOIUrl":"10.1016/j.actamat.2025.120930","url":null,"abstract":"<div><div>Metallic materials exhibiting ultrahigh strength coupled with exceptional ductility play a pivotal role in advanced industries, yet enhancing strength typically sacrifices strain hardening and ductility. This study presents a strategy that activated an innovative deformation mechanism to overcome the long-standing trade-off between strength and ductility in an L1<sub>2</sub>-strengthened Al<sub>5</sub>Ti<sub>8</sub>(FeCoNi)<sub>86.9</sub>B<sub>0.1</sub> high-entropy alloy. After aging at 765 °C for 4 hours, the alloy achieved a yield strength of 1227 MPa, an ultimate tensile strength of 1742 MPa, and an elongation of 39.9%, attributed to the ultrahigh and sustained strain hardening induced by phase transformation within dynamically refined microbands during deformation. Our findings indicated that FCC→BCC transformation within the microbands was more favorable in an FCC matrix with a larger width. Furthermore, a high density of superlattice intrinsic stacking faults and Lomer-Cottrell locks in L1<sub>2</sub> phase were formed, leading to additional strain hardening of the alloy. The synergistic interaction between phase transformation and microband formation offers a promising approach for designing novel high-performance alloys with exceptional strength and ductility.</div></div>","PeriodicalId":238,"journal":{"name":"Acta Materialia","volume":"289 ","pages":"Article 120930"},"PeriodicalIF":8.3,"publicationDate":"2025-03-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143599159","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 present work scrutinizes the trade-off between natural ageing stability time and formability achieved via preageing and two-step quenching in Al-Mg-Si alloys. Experimental analysis via resistivity and yield strength measurements and differential scanning calorimetry revealed that a prolonged isothermal hold period of 4 h at 100 °C is required to achieve natural aging stability via preageing. In contrast, an isothermal hold period of 1 h at 100 °C is sufficient to impart natural ageing stability via two-step quenching. Vacancy simulations revealed that the free vacancy concentration decreases during the isothermal hold period and equates the free vacancy concentration at 100 °C after an isothermal hold period of 4 h and 1 h for the preaging and two-step quenching route, respectively. The decrease in free vacancy concentration during the optimized isothermal hold periods causes reduced mobility of the solute atoms and suppression of natural ageing during the subsequent room temperature storage. Formability analysis revealed that on all forming indicators such as work hardening ability, strain rate sensitivity and fracture strains, the preaged sample outperforms the two-step quenched sample. An obstacle characteristics-based approach revealed that the higher dynamic recovery rate in the two-step quenched sample due to a relatively coarse precipitate structure is responsible for the impairment of the forming potential of the two-step quenched sample compared to the preaged sample. Based on vacancy and work-hardening simulations, a suitable thermomechanical processing route is proposed to produce a fine-grained microstructure, which reduces the natural aging stability time by 75 % without compromising the formability.
{"title":"A comprehensive examination of the formability-natural ageing stability time paradox in Al-Mg-Si alloys and developing mitigating pathways","authors":"Jyoti Ranjan Sahoo, Purnima Bharti, Aparna Tripathi, Sumeet Mishra","doi":"10.1016/j.actamat.2025.120927","DOIUrl":"10.1016/j.actamat.2025.120927","url":null,"abstract":"<div><div>The present work scrutinizes the trade-off between natural ageing stability time and formability achieved via preageing and two-step quenching in Al-Mg-Si alloys. Experimental analysis via resistivity and yield strength measurements and differential scanning calorimetry revealed that a prolonged isothermal hold period of 4 h at 100 °C is required to achieve natural aging stability via preageing. In contrast, an isothermal hold period of 1 h at 100 °C is sufficient to impart natural ageing stability via two-step quenching. Vacancy simulations revealed that the free vacancy concentration decreases during the isothermal hold period and equates the free vacancy concentration at 100 °C after an isothermal hold period of 4 h and 1 h for the preaging and two-step quenching route, respectively. The decrease in free vacancy concentration during the optimized isothermal hold periods causes reduced mobility of the solute atoms and suppression of natural ageing during the subsequent room temperature storage. Formability analysis revealed that on all forming indicators such as work hardening ability, strain rate sensitivity and fracture strains, the preaged sample outperforms the two-step quenched sample. An obstacle characteristics-based approach revealed that the higher dynamic recovery rate in the two-step quenched sample due to a relatively coarse precipitate structure is responsible for the impairment of the forming potential of the two-step quenched sample compared to the preaged sample. Based on vacancy and work-hardening simulations, a suitable thermomechanical processing route is proposed to produce a fine-grained microstructure, which reduces the natural aging stability time by 75 % without compromising the formability.</div></div>","PeriodicalId":238,"journal":{"name":"Acta Materialia","volume":"289 ","pages":"Article 120927"},"PeriodicalIF":8.3,"publicationDate":"2025-03-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143682976","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 : 2025-03-10DOI: 10.1016/j.actamat.2025.120922
G. Gengor , O.K. Celebi , A.S.K. Mohammed , H. Sehitoglu
To understand the role of defects in materials science, ranging from mechanical to physical properties, determining the spatial variation of elastic moduli is of paramount importance. Using electron wavefunctions, we derive novel expressions for local elastic moduli in the lattice scale, Quantum Mechanical Moduli Field (QMMF). The QMMF provides insight into the interplay between elastic properties and defects. To derive QMMF, we differentiate the local stress density against strain. The QMMF has contributions from kinetic, exchange-correlation, and electrostatic interactions. We provide novel expressions and numerical schemes to calculate QMMF. In atomistic calculations, the atoms are modeled as point-like entities, which only allows the macroscopic elastic properties to be calculated. Since the QMMF represents the local elastic properties, it provides a significant advancement from previous studies, especially in the presence of multi-elements. Four example applications of QMMF are provided. Firstly, the macroscopic elastic moduli of Ni and B2NiTi are calculated using QMMF in agreement with experiments. Secondly, a H interstitial in Ni is considered. The effect of H concentration on H softening is evaluated. Thirdly, the effect of dilatation on moduli is calculated, revealing the non-linearity of moduli. Finally, the local elastic properties around W solute in the Ni matrix are calculated. The W solute increases the macroscopic moduli of Ni in a non-linear fashion. It is found that the macroscopic hardening is due to the hardening of the Ni matrix rather than W solutes forming hard-spots. The QMMF uses electron densities to unveil such surprising effects that are otherwise unobservable.
{"title":"Quantum mechanical moduli field","authors":"G. Gengor , O.K. Celebi , A.S.K. Mohammed , H. Sehitoglu","doi":"10.1016/j.actamat.2025.120922","DOIUrl":"10.1016/j.actamat.2025.120922","url":null,"abstract":"<div><div>To understand the role of defects in materials science, ranging from mechanical to physical properties, determining the spatial variation of elastic moduli is of paramount importance. Using electron wavefunctions, we derive novel expressions for local elastic moduli in the lattice scale, Quantum Mechanical Moduli Field (QMMF). The QMMF provides insight into the interplay between elastic properties and defects. To derive QMMF, we differentiate the local stress density against strain. The QMMF has contributions from kinetic, exchange-correlation, and electrostatic interactions. We provide novel expressions and numerical schemes to calculate QMMF. In atomistic calculations, the atoms are modeled as point-like entities, which only allows the macroscopic elastic properties to be calculated. Since the QMMF represents the local elastic properties, it provides a significant advancement from previous studies, especially in the presence of multi-elements. Four example applications of QMMF are provided. Firstly, the macroscopic elastic moduli of Ni and B2NiTi are calculated using QMMF in agreement with experiments. Secondly, a H interstitial in Ni is considered. The effect of H concentration on H softening is evaluated. Thirdly, the effect of dilatation on moduli is calculated, revealing the non-linearity of moduli. Finally, the local elastic properties around W solute in the Ni matrix are calculated. The W solute increases the macroscopic moduli of Ni in a non-linear fashion. It is found that the macroscopic hardening is due to the hardening of the Ni matrix rather than W solutes forming hard-spots. The QMMF uses electron densities to unveil such surprising effects that are otherwise unobservable.</div></div>","PeriodicalId":238,"journal":{"name":"Acta Materialia","volume":"289 ","pages":"Article 120922"},"PeriodicalIF":8.3,"publicationDate":"2025-03-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143618491","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 : 2025-03-10DOI: 10.1016/j.actamat.2025.120928
Xiaochong Lu , Yilun Xu , Hao Ran , Guohua Fan , Si Gao , Nobuhiro Tsuji , Chongxiang Huang , Huajian Gao , Yong-Wei Zhang
Heterostructured materials, characterized by distinct zones with varying mechanical properties, offer a promising strategy to overcome the traditional strength-ductility trade-off in metallic materials. In this study, we focus on heterostructured materials composed of hard and soft metallic layers, investigating the effect of the layer strength ratio (R) on strain hardening in these materials. Using a combination of experimental techniques, crystal plasticity finite element (CPFE) simulations, and discrete dislocation plasticity (DDP) simulations, we explore how R influences the accumulation of geometrically necessary dislocations (GNDs) and the associated stress field at the hetero-zone boundary (HB). Our findings reveal that deformation inhomogeneity between the soft and hard zones generates significant strain gradients near the HBs, leading to enhanced strain hardening through intensified dislocation pile-up and long-range internal stress. Increasing the layer strength ratio R amplifies the deformation inhomogeneity near the HBs, resulting in substantial strain hardening. Additionally, HB density is shown to be another tunable parameter that, when optimized, can significantly enhance strain hardening. This work establishes a quantitative framework for understanding the relationship between layer strength ratio R and strain hardening, offering valuable insights for optimizing the strength-ductility synergy in heterostructured materials.
{"title":"The role of layer strength ratio in enhancing strain hardening and achieving strength-ductility synergy in heterostructured materials","authors":"Xiaochong Lu , Yilun Xu , Hao Ran , Guohua Fan , Si Gao , Nobuhiro Tsuji , Chongxiang Huang , Huajian Gao , Yong-Wei Zhang","doi":"10.1016/j.actamat.2025.120928","DOIUrl":"10.1016/j.actamat.2025.120928","url":null,"abstract":"<div><div>Heterostructured materials, characterized by distinct zones with varying mechanical properties, offer a promising strategy to overcome the traditional strength-ductility trade-off in metallic materials. In this study, we focus on heterostructured materials composed of hard and soft metallic layers, investigating the effect of the layer strength ratio (<em>R</em>) on strain hardening in these materials. Using a combination of experimental techniques, crystal plasticity finite element (CPFE) simulations, and discrete dislocation plasticity (DDP) simulations, we explore how <em>R</em> influences the accumulation of geometrically necessary dislocations (GNDs) and the associated stress field at the hetero-zone boundary (HB). Our findings reveal that deformation inhomogeneity between the soft and hard zones generates significant strain gradients near the HBs, leading to enhanced strain hardening through intensified dislocation pile-up and long-range internal stress. Increasing the layer strength ratio <em>R</em> amplifies the deformation inhomogeneity near the HBs, resulting in substantial strain hardening. Additionally, HB density is shown to be another tunable parameter that, when optimized, can significantly enhance strain hardening. This work establishes a quantitative framework for understanding the relationship between layer strength ratio <em>R</em> and strain hardening, offering valuable insights for optimizing the strength-ductility synergy in heterostructured materials.</div></div>","PeriodicalId":238,"journal":{"name":"Acta Materialia","volume":"289 ","pages":"Article 120928"},"PeriodicalIF":8.3,"publicationDate":"2025-03-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143643998","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 : 2025-03-09DOI: 10.1016/j.actamat.2025.120887
H.C. Howard , W.S. Cunningham , A. Genc , B.E. Rhodes , B. Merle , T.J. Rupert , D.S. Gianola
There is emerging recognition that crystalline defects such as grain boundaries and dislocations can host structural and chemical environments of their own, which reside in local equilibrium with the bulk material. Targeting these defect phases as objects for materials design would promise new avenues to maximize property gains. Here, we provide experimental proof of a dislocation-templated defect phase using a processing strategy designed to engender defect phase transitions in a nickel-based alloy and demonstrate dramatic effects on strengthening. Following heat treatments designed to encourage solute segregation to dislocations, regions with introduced dislocation populations show evidence of nanoscale ordered domains with a L1 structure, whereas dislocation-free regions remain as a solid solution. Site-specific spherical nanoindentation in regions hosting dislocations and their associated ordered nanodomains exhibit a 40% increase in mean pop-in load compared to similar regions prior to the segregation heat treatment. Strength estimates based on random solute atmospheres around dislocations are not sufficient to predict our measured strengths. Our mechanical measurements, in tandem with detailed electron microscopy and diffraction of the ordered domains, as well as characterization of dislocations in the vicinity of the nanodomains, establish the defect phase framework via direct observations of chemical and structural ordering near dislocations and its potential for offering favorable properties not achievable through conventional materials design.
{"title":"Chemically ordered dislocation defect phases as a new strengthening pathway in Ni–Al alloys","authors":"H.C. Howard , W.S. Cunningham , A. Genc , B.E. Rhodes , B. Merle , T.J. Rupert , D.S. Gianola","doi":"10.1016/j.actamat.2025.120887","DOIUrl":"10.1016/j.actamat.2025.120887","url":null,"abstract":"<div><div>There is emerging recognition that crystalline defects such as grain boundaries and dislocations can host structural and chemical environments of their own, which reside in local equilibrium with the bulk material. Targeting these defect phases as objects for materials design would promise new avenues to maximize property gains. Here, we provide experimental proof of a dislocation-templated defect phase using a processing strategy designed to engender defect phase transitions in a nickel-based alloy and demonstrate dramatic effects on strengthening. Following heat treatments designed to encourage solute segregation to dislocations, regions with introduced dislocation populations show evidence of nanoscale ordered domains with a <em>L</em>1<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span> structure, whereas dislocation-free regions remain as a solid solution. Site-specific spherical nanoindentation in regions hosting dislocations and their associated ordered nanodomains exhibit a 40% increase in mean pop-in load compared to similar regions prior to the segregation heat treatment. Strength estimates based on random solute atmospheres around dislocations are not sufficient to predict our measured strengths. Our mechanical measurements, in tandem with detailed electron microscopy and diffraction of the ordered domains, as well as characterization of dislocations in the vicinity of the nanodomains, establish the defect phase framework via direct observations of chemical and structural ordering near dislocations and its potential for offering favorable properties not achievable through conventional materials design.</div></div>","PeriodicalId":238,"journal":{"name":"Acta Materialia","volume":"289 ","pages":"Article 120887"},"PeriodicalIF":8.3,"publicationDate":"2025-03-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143576325","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 : 2025-03-09DOI: 10.1016/j.actamat.2025.120919
Qianwei Guo , Hanghang Liu , Chen Sun , Yanfei Cao , Xingyu Lu , Yinuo Du , Xinyu Ru , Haitao Xu , Kaiyan Song , Paixian Fu , Dianzhong Li
Gradient structures can significantly enhance the wear resistance of steels through the synergistic effects of heterogeneity. However, traditional surface heterostructures typically produce a single gradient. Here, we propose a novel strategy to implement a dual-gradient structure of composition and nanocrystalline, thereby enhancing the wear resistance of bearing steel by suppressing strain localization. The compositional gradient prefabricated by carburization facilitates the formation of gradient-distributed carbides and martensite, while the nanocrystalline gradient is developed further via ultrasonic shot peening. Strong dislocation movement promotes the refinement and decomposition of large-sized irregular carbides in the surface layer, significantly mitigating the initiation and propagation of cracks induced by stress localization. Additionally, the numerous nanograins in the surface layer not only contribute to the formation of a more stable and dense oxide film under oil lubrication but also create a more dispersed region of stress localization by co-sharing cyclic shear stress, thereby alleviating sliding-induced microstructural instability. Furthermore, the single compositional gradient structure tends to surface strain localization during loading, attributable to the relatively gradual transition between the hard and soft layers, whereas the dual-gradient structure facilitates surface strain delocalization across a wider stress range due to the presence of numerous nanograins creating a more pronounced strain gradient. Compared to the single compositional gradient, the unique dual-gradient structure reduces the wear rate by 52.5 % and 53.9 % at low and high-frequency sliding, respectively. This work proposes a promising design for the fabrication of dual-gradient structures to enhance the wear resistance in high-strength steels.
{"title":"Dual-gradient structure enhances wear resistance of aero-engine bearing steel by suppressing strain localization","authors":"Qianwei Guo , Hanghang Liu , Chen Sun , Yanfei Cao , Xingyu Lu , Yinuo Du , Xinyu Ru , Haitao Xu , Kaiyan Song , Paixian Fu , Dianzhong Li","doi":"10.1016/j.actamat.2025.120919","DOIUrl":"10.1016/j.actamat.2025.120919","url":null,"abstract":"<div><div>Gradient structures can significantly enhance the wear resistance of steels through the synergistic effects of heterogeneity. However, traditional surface heterostructures typically produce a single gradient. Here, we propose a novel strategy to implement a dual-gradient structure of composition and nanocrystalline, thereby enhancing the wear resistance of bearing steel by suppressing strain localization. The compositional gradient prefabricated by carburization facilitates the formation of gradient-distributed carbides and martensite, while the nanocrystalline gradient is developed further via ultrasonic shot peening. Strong dislocation movement promotes the refinement and decomposition of large-sized irregular carbides in the surface layer, significantly mitigating the initiation and propagation of cracks induced by stress localization. Additionally, the numerous nanograins in the surface layer not only contribute to the formation of a more stable and dense oxide film under oil lubrication but also create a more dispersed region of stress localization by co-sharing cyclic shear stress, thereby alleviating sliding-induced microstructural instability. Furthermore, the single compositional gradient structure tends to surface strain localization during loading, attributable to the relatively gradual transition between the hard and soft layers, whereas the dual-gradient structure facilitates surface strain delocalization across a wider stress range due to the presence of numerous nanograins creating a more pronounced strain gradient. Compared to the single compositional gradient, the unique dual-gradient structure reduces the wear rate by 52.5 % and 53.9 % at low and high-frequency sliding, respectively. This work proposes a promising design for the fabrication of dual-gradient structures to enhance the wear resistance in high-strength steels.</div></div>","PeriodicalId":238,"journal":{"name":"Acta Materialia","volume":"289 ","pages":"Article 120919"},"PeriodicalIF":8.3,"publicationDate":"2025-03-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143576234","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 : 2025-03-08DOI: 10.1016/j.actamat.2025.120886
Alvaro Martinez-Pechero , Eralp Demir , Chris Hardie , Yevhen Zayachuk , Anna Widdowson , Edmund Tarleton
This research utilizes established cyclic deformation models to simulate the Bauschinger effect observed in copper monocrystal cantilever experiments during the initial bending and straightening phases. Crystal plasticity finite element simulations employing Armstrong-Frederick, Orowan-Sleeswyk, and various other backstress models have drawbacks to reproduce the experimental force–displacement curves accurately since they are not able to reproduce the isotropic hardening measured during cantilever straightening. However, the Armstrong-Frederick model combined with Voce-type hardening and a newly proposed modified Orowan-Sleeswyk model has proven to be effective. In this work, we propose a modified Orowan-Sleeswyk model, based on recent studies, where not all the geometrically necessary dislocations (GND) recombine during the straightening phase, but instead reorient to achieve a net zero-strain gradient with ongoing hardening during load reversal.
{"title":"Modelling the Bauschinger effect in copper during preliminary load cycles","authors":"Alvaro Martinez-Pechero , Eralp Demir , Chris Hardie , Yevhen Zayachuk , Anna Widdowson , Edmund Tarleton","doi":"10.1016/j.actamat.2025.120886","DOIUrl":"10.1016/j.actamat.2025.120886","url":null,"abstract":"<div><div>This research utilizes established cyclic deformation models to simulate the Bauschinger effect observed in copper monocrystal cantilever experiments during the initial bending and straightening phases. Crystal plasticity finite element simulations employing <em>Armstrong-Frederick</em>, <em>Orowan-Sleeswyk</em>, and various other backstress models have drawbacks to reproduce the experimental force–displacement curves accurately since they are not able to reproduce the isotropic hardening measured during cantilever straightening. However, the <em>Armstrong-Frederick</em> model combined with <em>Voce-type hardening</em> and a newly proposed <em>modified Orowan-Sleeswyk</em> model has proven to be effective. In this work, we propose a <em>modified Orowan-Sleeswyk</em> model, based on recent studies, where not all the geometrically necessary dislocations (GND) recombine during the straightening phase, but instead reorient to achieve a net zero-strain gradient with ongoing hardening during load reversal.</div></div>","PeriodicalId":238,"journal":{"name":"Acta Materialia","volume":"289 ","pages":"Article 120886"},"PeriodicalIF":8.3,"publicationDate":"2025-03-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143576235","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}
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