Integrating a heterogeneous structure can significantly enhance the strength-ductility synergy of composites.However,the relationship between hetero-deformation induced(HDI)strain hardening and dislocation activity ca...Integrating a heterogeneous structure can significantly enhance the strength-ductility synergy of composites.However,the relationship between hetero-deformation induced(HDI)strain hardening and dislocation activity caused by heterogeneous structures in the magnesium matrix composite remains unclear.In this study,a dual-heterogeneous TiC/AZ61 composite exhibits significantly improved plastic elongation(PEL)by nearly one time compared to uniform FG composite,meanwhile maintaining a high strength(UTS:417 MPa).This is because more severe deformation inhomogeneity in heterogeneous structure leads to more geometrically necessary dislocations(GNDs)accumulation and stronger HDI stress,resulting in higher HDI hardening compared to FG and CG composites.During the early stage of plastic deformation,the pile-up types of GND in the FG zone and CG zone are significantly different.GNDs tend to form substructures in the FG zone instead of the CG zone.They only accumulate at grain boundaries of the CG region,thereby leading to obviously increased back stress in the CG region.In the late deformation stage,the elevated HDI stress activates the new〈c+a〉dislocations in the CG region,resulting in dislocation entanglements and even the formation of substructures,further driving the high hardening in the heterogeneous composite.However,For CG composite,〈c+a〉dislocations are not activated even under large plastic strains,and only〈a〉dislocations pile up at grain boundaries and twin boundaries.Our work provides an in-depth understanding of dislocation variation and HDI hardening in heterogeneous magnesium-based composites.展开更多
The plastic deformation of semiconductors,a process critical to their mechanical and electronic properties,involves various mechanisms such as dislocation motion and phase transition.Here,we systematically examined th...The plastic deformation of semiconductors,a process critical to their mechanical and electronic properties,involves various mechanisms such as dislocation motion and phase transition.Here,we systematically examined the temperature-dependent Peierls stress for 30°and 90°partial dislocations in cadmium telluride(CdTe),using a combination of molecular statics and molecular dynamics simulations with a machine-learning force field,as well as density functional theory simulations.Our findings reveal that the 0 K Peierls stresses for these partial dislocations in CdTe are relatively low,ranging from 0.52 GPa to 1.46 GPa,due to its significant ionic bonding characteristics.Notably,in the CdTe system containing either a 30°Cd-core or 90°Te-core partial dislocation,a phase transition from the zinc-blende phase to theβ-Sn-like phase is favored over dislocation motion.This suggests a competitive relationship between these two mechanisms,driven by the bonding characteristics within the dislocation core and the relatively low phase transition stress of∼1.00 GPa.Furthermore,we observed a general trend wherein the Peierls stress for partial dislocations in CdTe exhibits a temperature dependence,which decreases with increasing temperature,becoming lower than the phase transition stress at elevated temperatures.Consequently,the dominant deformation mechanism in CdTe shifts from solid-state phase transition at low temperatures to dislocation motion at high temperatures.This investigation uncovers a compelling interplay between dislocation motion and phase transition in the plastic deformation of CdTe,offering profound insights into the mechanical behavior and electronic performance of CdTe and other II-VI semiconductors.展开更多
Dislocations and disclinations are fundamental topological defects within crystals,which determine the mechanical properties of metals and alloys.Despite their important roles in multiple physical mechanisms,e.g.,dyna...Dislocations and disclinations are fundamental topological defects within crystals,which determine the mechanical properties of metals and alloys.Despite their important roles in multiple physical mechanisms,e.g.,dynamic recovery and grain boundary mediated plasticity,the intrinsic coupling and correlation between disclinations and dislocations,and their impacts on the deformation behavior of metallic materials still remain obscure,partially due to the lack of a theoretical tool to capture the rotational nature of disclinations.By using a Lie-algebra-based theoretical framework,we obtain a general equation to quantify the intrinsic coupling of disclinations and dislocations.Through quasi in-situ electron backscatter diffraction characterizations and disclination/dislocation density analyses in Mg alloys,the generation,coevolution and reactions of disclinations and dislocations during dynamic recovery and superplastic deformation have been quantitatively analyzed.It has been demonstrated that the obtained governing equation can capture multiple physical processes associated with mechanical deformation of metals,e.g.,grain rotation and grain boundary migration,at both room temperature and high temperature.By establishing the disclination-dislocation coupling equation within a Lie algebra description,our work provides new insights for exploring the coevolution and reaction of disclinations/dislocations,with profound implications for elucidating the microstructure-property relationship and underlying deformation mechanisms in metallic materials.展开更多
Elbow dislocations are rare injuries in children due to the resistance of the capsuloligamentous structures. Anterior dislocation is very rare and its combination with an olecranon fracture is unusual. The authors rep...Elbow dislocations are rare injuries in children due to the resistance of the capsuloligamentous structures. Anterior dislocation is very rare and its combination with an olecranon fracture is unusual. The authors report a case of this lesion in a 7-year-old child managed nonoperatively.展开更多
Lutetium oxide(Lu_(2)O_(3))is recognized as a potential laser crystal material,and it is noted for its high ther⁃mal conductivity,low phonon energy,and strong crystal field.Nevertheless,its high melting point of 2450...Lutetium oxide(Lu_(2)O_(3))is recognized as a potential laser crystal material,and it is noted for its high ther⁃mal conductivity,low phonon energy,and strong crystal field.Nevertheless,its high melting point of 2450℃induces significant temperature gradients,resulting in a proliferation of defects.The scarcity of comprehensive research on this crystal’s defects hinders the enhancement of crystal quality.In this study,we employed the chemical etching method to examine the etching effects on Lu_(2)O_(3)crystals under various conditions and to identify the optimal conditions for investi⁃gating the dislocation defects of Lu_(2)O_(3)crystals(mass fraction 70%H3PO4,160℃,15-18 min).The morphologies of dislocation etch pits on the(111)-and(110)-oriented Lu_(2)O_(3)wafers were characterized using microscopy,scanning electron microscopy and atomic force microscopy.This research addresses the gap in understanding Lu_(2)O_(3)line defects and offers guidance for optimizing the crystal growth process and improving crystal quality.展开更多
Objective: The present research aims to determine if adherence to the Lewinnek safe zone, when exclusively considered, constitutes a pivotal element for ensuring stability in the context of total hip arthroplasty. Thi...Objective: The present research aims to determine if adherence to the Lewinnek safe zone, when exclusively considered, constitutes a pivotal element for ensuring stability in the context of total hip arthroplasty. This is done by examining the acetabular placement in instances of hip dislocation after total hip arthroplasty (THA). Methodology: The authors searched 2653 patient records from 2015 to 2022 looking for patients who had total hip arthroplasty at our facility. For the analysis, 23 patients were culled from 64 individuals who exhibited post-THA dislocations, employing a stringent exclusion criterion, and the resultant acetabular angulation and anteversion were quantified utilizing PEEKMED software (Peek Health S.A., Portugal) upon radiographic evidence. Results: Within the operational timeframe, from the cohort of 2653 subjects, 64 presented with at least a singular incident of displacement. Post-exclusion criterion enforcement, 23 patients were eligible for inclusion. Of these, 10 patients conformed to the safe zone demarcated by Lewinnek for both inclination and anteversion angles, while 13 exhibited deviations from the prescribed anteversion and/or inclination benchmarks. Conclusion: Analysis of the 23 patients reveals that 13 did not confirm to be in the safe zone parameters for anteversion and/or inclination, whereas 10 were within the safe zone as per Lewinnek’s guidelines. This investigative review, corroborated by extant literature, suggests that the isolated consideration of the Lewinnek safe zone does not suffice as a solitary protective factor. It further posits that additional variables are equally critical as acetabular positioning and mandate individual assessment.展开更多
This study investigates the effect of high current density electropulsing on the material in a rapid stress relaxation process.An AISI 1020 steel was shot-peened to induce surface compressive residual stresses in a co...This study investigates the effect of high current density electropulsing on the material in a rapid stress relaxation process.An AISI 1020 steel was shot-peened to induce surface compressive residual stresses in a controlled manner and subsequently electropulsed to investigate the changes in microstructure and defect configuration.AISI 1020 steel was chosen as it has a simple microstructure(plain ferritic)and composition with low alloying conditions.It is an appropriate material to study the effect of trans-mitting electric pulses on the microstructural defect evolution.A combination of electron-backscattered diffraction and transmission electron microscopy proved to be an effective tool in characterizing the post-electropulsing effects critically.By application of electropulsing,a reduction in the surface residual stress layer was noticed.Also,reductions in misorientation and dislocation density together with the disentan-glement of dislocations within the cold-worked layer were observed after electropulsing.Additionally,the annihilation of shot-peening-induced deformation bands beyond the residual layer depth was observed.These effects have been rationalised by taking into account the various possibilities of athermal effects of electropulsing.展开更多
Spurious forces are a significant challenge for multi-scale methods,e.g.,the coupled atomistic/discrete dislocation(CADD)method.The assumption of isotropic matter in the continuum domain is a critical factor leading t...Spurious forces are a significant challenge for multi-scale methods,e.g.,the coupled atomistic/discrete dislocation(CADD)method.The assumption of isotropic matter in the continuum domain is a critical factor leading to such forces.This study aims to minimize spurious forces,ensuring that atomic dislocations experience more precise forces from the continuum domain.The authors have already implemented this idea using a simplified and unrealistic slipping system.To create a comprehensive and realistic model,this paper considers all possible slip systems in the face center cubic(FCC)lattice structure,and derives the required relationships for the displacement fields.An anisotropic version of the three-dimensional CADD(CADD3D)method is presented,which generates the anisotropic displacement fields for the partial dislocations in all the twelve slip systems of the FCC lattice structure.These displacement fields are tested for the most probable slip systems of aluminum,nickel,and copper with different anisotropic levels.Implementing these anisotropic displacement fields significantly reduces the spurious forces on the slip systems of FCC materials.This improvement is particularly pronounced at greater distances from the interface and in more anisotropic materials.Furthermore,the anisotropic CADD3D method enhances the spurious stress difference between the slip systems,particularly for materials with higher anisotropy.展开更多
There is a pressing need for high-performance,high-strength low-alloy structural(HSLA)steels in various engineering fields,such as hydraulic components,engineering machinery,bridges,ships,and pressure vessels.In this ...There is a pressing need for high-performance,high-strength low-alloy structural(HSLA)steels in various engineering fields,such as hydraulic components,engineering machinery,bridges,ships,and pressure vessels.In this study,a gradient dislocation-cell structure is introduced into an HSLA steel through ultrasonic severe surface rolling.The cell size is approximately 614 nm at the topmost surface layer,and increases with increasing the depth.Most of the cell walls have a misorientation ranging from 2°to 15°,indicating they belong to low angle grain boundaries(LAGBs),while some cell walls have a misorientation of less than 2°,corresponding to dense dislocation walls(DDWs).This unique gradient structure offers an exceptional combination of strength and ductility,with a high yield strength of 522.3±1.4 MPa and an accepted elongation of 25.5±1.7%.The morphology and size of the dislocation cells remain remarkably stable after uniaxial tension,demonstrating their efficacy as effective barriers hindering dislocation movement and thus enhancing strength and hardness.This gradient dislocation-cell structure facilitates inhomogeneous plastic deformation during uniaxial tensile loading,resulting in a pronounced accumulation of geometrically necessary dislocations(GNDs).These GNDs play a significant role in conferring favorable mechanical properties by inducing hetero-deformation-induced(HDI)strengthening effects and forest hardening effects.This study presents a promising avenue for achieving the desired mechanical properties in HSLA steel.展开更多
基金support from the National Natural Science Foundation of China(No:52061040)China Postdoctoral Science Foundation(No:2021M692512)+1 种基金Opening Project of Material Corrosion and Protection Key Laboratory of Sichuan Province(No:2023CL01)Open Projects of Key Laboratory of Advanced Technologies of Materials,Ministry of Education China,Southwest Jiaotong University(No:KLATM202003).
文摘Integrating a heterogeneous structure can significantly enhance the strength-ductility synergy of composites.However,the relationship between hetero-deformation induced(HDI)strain hardening and dislocation activity caused by heterogeneous structures in the magnesium matrix composite remains unclear.In this study,a dual-heterogeneous TiC/AZ61 composite exhibits significantly improved plastic elongation(PEL)by nearly one time compared to uniform FG composite,meanwhile maintaining a high strength(UTS:417 MPa).This is because more severe deformation inhomogeneity in heterogeneous structure leads to more geometrically necessary dislocations(GNDs)accumulation and stronger HDI stress,resulting in higher HDI hardening compared to FG and CG composites.During the early stage of plastic deformation,the pile-up types of GND in the FG zone and CG zone are significantly different.GNDs tend to form substructures in the FG zone instead of the CG zone.They only accumulate at grain boundaries of the CG region,thereby leading to obviously increased back stress in the CG region.In the late deformation stage,the elevated HDI stress activates the new〈c+a〉dislocations in the CG region,resulting in dislocation entanglements and even the formation of substructures,further driving the high hardening in the heterogeneous composite.However,For CG composite,〈c+a〉dislocations are not activated even under large plastic strains,and only〈a〉dislocations pile up at grain boundaries and twin boundaries.Our work provides an in-depth understanding of dislocation variation and HDI hardening in heterogeneous magnesium-based composites.
基金supported by the National Science Foundation(No.CMMI-2019459).
文摘The plastic deformation of semiconductors,a process critical to their mechanical and electronic properties,involves various mechanisms such as dislocation motion and phase transition.Here,we systematically examined the temperature-dependent Peierls stress for 30°and 90°partial dislocations in cadmium telluride(CdTe),using a combination of molecular statics and molecular dynamics simulations with a machine-learning force field,as well as density functional theory simulations.Our findings reveal that the 0 K Peierls stresses for these partial dislocations in CdTe are relatively low,ranging from 0.52 GPa to 1.46 GPa,due to its significant ionic bonding characteristics.Notably,in the CdTe system containing either a 30°Cd-core or 90°Te-core partial dislocation,a phase transition from the zinc-blende phase to theβ-Sn-like phase is favored over dislocation motion.This suggests a competitive relationship between these two mechanisms,driven by the bonding characteristics within the dislocation core and the relatively low phase transition stress of∼1.00 GPa.Furthermore,we observed a general trend wherein the Peierls stress for partial dislocations in CdTe exhibits a temperature dependence,which decreases with increasing temperature,becoming lower than the phase transition stress at elevated temperatures.Consequently,the dominant deformation mechanism in CdTe shifts from solid-state phase transition at low temperatures to dislocation motion at high temperatures.This investigation uncovers a compelling interplay between dislocation motion and phase transition in the plastic deformation of CdTe,offering profound insights into the mechanical behavior and electronic performance of CdTe and other II-VI semiconductors.
基金Financial supports from the National Natural Science Foundation of China(Nos.52171116,U22A20109,52334010 and T2325013)are greatly acknowledgedPartial financial support came from The Program for the Central University Youth Innovation Team,and the Fundamental Research Funds for the Central Universities,JLU.
文摘Dislocations and disclinations are fundamental topological defects within crystals,which determine the mechanical properties of metals and alloys.Despite their important roles in multiple physical mechanisms,e.g.,dynamic recovery and grain boundary mediated plasticity,the intrinsic coupling and correlation between disclinations and dislocations,and their impacts on the deformation behavior of metallic materials still remain obscure,partially due to the lack of a theoretical tool to capture the rotational nature of disclinations.By using a Lie-algebra-based theoretical framework,we obtain a general equation to quantify the intrinsic coupling of disclinations and dislocations.Through quasi in-situ electron backscatter diffraction characterizations and disclination/dislocation density analyses in Mg alloys,the generation,coevolution and reactions of disclinations and dislocations during dynamic recovery and superplastic deformation have been quantitatively analyzed.It has been demonstrated that the obtained governing equation can capture multiple physical processes associated with mechanical deformation of metals,e.g.,grain rotation and grain boundary migration,at both room temperature and high temperature.By establishing the disclination-dislocation coupling equation within a Lie algebra description,our work provides new insights for exploring the coevolution and reaction of disclinations/dislocations,with profound implications for elucidating the microstructure-property relationship and underlying deformation mechanisms in metallic materials.
文摘Elbow dislocations are rare injuries in children due to the resistance of the capsuloligamentous structures. Anterior dislocation is very rare and its combination with an olecranon fracture is unusual. The authors report a case of this lesion in a 7-year-old child managed nonoperatively.
基金Supported by National Key Research and Development Program of China(2021YFB3601403)National Natural Science Foundation of China(62105181)Taishan Scholar of Shandong Province(tsqn202306014)。
文摘Lutetium oxide(Lu_(2)O_(3))is recognized as a potential laser crystal material,and it is noted for its high ther⁃mal conductivity,low phonon energy,and strong crystal field.Nevertheless,its high melting point of 2450℃induces significant temperature gradients,resulting in a proliferation of defects.The scarcity of comprehensive research on this crystal’s defects hinders the enhancement of crystal quality.In this study,we employed the chemical etching method to examine the etching effects on Lu_(2)O_(3)crystals under various conditions and to identify the optimal conditions for investi⁃gating the dislocation defects of Lu_(2)O_(3)crystals(mass fraction 70%H3PO4,160℃,15-18 min).The morphologies of dislocation etch pits on the(111)-and(110)-oriented Lu_(2)O_(3)wafers were characterized using microscopy,scanning electron microscopy and atomic force microscopy.This research addresses the gap in understanding Lu_(2)O_(3)line defects and offers guidance for optimizing the crystal growth process and improving crystal quality.
文摘Objective: The present research aims to determine if adherence to the Lewinnek safe zone, when exclusively considered, constitutes a pivotal element for ensuring stability in the context of total hip arthroplasty. This is done by examining the acetabular placement in instances of hip dislocation after total hip arthroplasty (THA). Methodology: The authors searched 2653 patient records from 2015 to 2022 looking for patients who had total hip arthroplasty at our facility. For the analysis, 23 patients were culled from 64 individuals who exhibited post-THA dislocations, employing a stringent exclusion criterion, and the resultant acetabular angulation and anteversion were quantified utilizing PEEKMED software (Peek Health S.A., Portugal) upon radiographic evidence. Results: Within the operational timeframe, from the cohort of 2653 subjects, 64 presented with at least a singular incident of displacement. Post-exclusion criterion enforcement, 23 patients were eligible for inclusion. Of these, 10 patients conformed to the safe zone demarcated by Lewinnek for both inclination and anteversion angles, while 13 exhibited deviations from the prescribed anteversion and/or inclination benchmarks. Conclusion: Analysis of the 23 patients reveals that 13 did not confirm to be in the safe zone parameters for anteversion and/or inclination, whereas 10 were within the safe zone as per Lewinnek’s guidelines. This investigative review, corroborated by extant literature, suggests that the isolated consideration of the Lewinnek safe zone does not suffice as a solitary protective factor. It further posits that additional variables are equally critical as acetabular positioning and mandate individual assessment.
基金supported by the National Research Foundation of Singapore,Rolls-Royce Singapore Pte.Ltd.,and Nanyang Technological University through grants#002123-00009 and #002124-00009.
文摘This study investigates the effect of high current density electropulsing on the material in a rapid stress relaxation process.An AISI 1020 steel was shot-peened to induce surface compressive residual stresses in a controlled manner and subsequently electropulsed to investigate the changes in microstructure and defect configuration.AISI 1020 steel was chosen as it has a simple microstructure(plain ferritic)and composition with low alloying conditions.It is an appropriate material to study the effect of trans-mitting electric pulses on the microstructural defect evolution.A combination of electron-backscattered diffraction and transmission electron microscopy proved to be an effective tool in characterizing the post-electropulsing effects critically.By application of electropulsing,a reduction in the surface residual stress layer was noticed.Also,reductions in misorientation and dislocation density together with the disentan-glement of dislocations within the cold-worked layer were observed after electropulsing.Additionally,the annihilation of shot-peening-induced deformation bands beyond the residual layer depth was observed.These effects have been rationalised by taking into account the various possibilities of athermal effects of electropulsing.
文摘Spurious forces are a significant challenge for multi-scale methods,e.g.,the coupled atomistic/discrete dislocation(CADD)method.The assumption of isotropic matter in the continuum domain is a critical factor leading to such forces.This study aims to minimize spurious forces,ensuring that atomic dislocations experience more precise forces from the continuum domain.The authors have already implemented this idea using a simplified and unrealistic slipping system.To create a comprehensive and realistic model,this paper considers all possible slip systems in the face center cubic(FCC)lattice structure,and derives the required relationships for the displacement fields.An anisotropic version of the three-dimensional CADD(CADD3D)method is presented,which generates the anisotropic displacement fields for the partial dislocations in all the twelve slip systems of the FCC lattice structure.These displacement fields are tested for the most probable slip systems of aluminum,nickel,and copper with different anisotropic levels.Implementing these anisotropic displacement fields significantly reduces the spurious forces on the slip systems of FCC materials.This improvement is particularly pronounced at greater distances from the interface and in more anisotropic materials.Furthermore,the anisotropic CADD3D method enhances the spurious stress difference between the slip systems,particularly for materials with higher anisotropy.
基金Supported by National Natural Science Foundation of China(Grant No.U1910212)the Priority Academic Program Development of Jiangsu Higher Education Institutions。
文摘There is a pressing need for high-performance,high-strength low-alloy structural(HSLA)steels in various engineering fields,such as hydraulic components,engineering machinery,bridges,ships,and pressure vessels.In this study,a gradient dislocation-cell structure is introduced into an HSLA steel through ultrasonic severe surface rolling.The cell size is approximately 614 nm at the topmost surface layer,and increases with increasing the depth.Most of the cell walls have a misorientation ranging from 2°to 15°,indicating they belong to low angle grain boundaries(LAGBs),while some cell walls have a misorientation of less than 2°,corresponding to dense dislocation walls(DDWs).This unique gradient structure offers an exceptional combination of strength and ductility,with a high yield strength of 522.3±1.4 MPa and an accepted elongation of 25.5±1.7%.The morphology and size of the dislocation cells remain remarkably stable after uniaxial tension,demonstrating their efficacy as effective barriers hindering dislocation movement and thus enhancing strength and hardness.This gradient dislocation-cell structure facilitates inhomogeneous plastic deformation during uniaxial tensile loading,resulting in a pronounced accumulation of geometrically necessary dislocations(GNDs).These GNDs play a significant role in conferring favorable mechanical properties by inducing hetero-deformation-induced(HDI)strengthening effects and forest hardening effects.This study presents a promising avenue for achieving the desired mechanical properties in HSLA steel.
