Tensile properties, fracture characteristics and microstructures of 7055 aluminum-based alloy containing Ag after T6, T73 and RRA treatment were investigated. The results show that RRA treatment retains strength of 70...Tensile properties, fracture characteristics and microstructures of 7055 aluminum-based alloy containing Ag after T6, T73 and RRA treatment were investigated. The results show that RRA treatment retains strength of 7055-T6 with higher electrical conductivity close to that of 7055-T73 alloy, but its elongation decreases greatly. SEM fractographs reveal that intergranular cracking and shear-type transgranular cracking are both presented on the fracture appearance of 7055-T6 specimen. After T73 treatment, the fractographs mainly consist of dimple-type transgranular cracking with minor intergranular cracking. For 7055-RRA specimen, intergranular cracking dominates with minor dimples on the fracture surface. The type and size of precipitates, width of grain boundary and the ability of precipitates to impede dislocation motion vary with heat treatment regimes. Three frature models were built on the basis of microstructural analyses.展开更多
Back stress has been proven to be the primary mechanism for superior mechanical properties of heterogeneous structures,but its quantitative contribution remains vague.The main purpose of this work is to clarify the co...Back stress has been proven to be the primary mechanism for superior mechanical properties of heterogeneous structures,but its quantitative contribution remains vague.The main purpose of this work is to clarify the contributions of back stress components,i.e.,intergranular residual stress and intragranular back stress,to the mechanical properties of heterogeneous structures based on the crystal plasticity theory.The results show that the intragranular back stress is smaller than the intergranular residual stress but contributes significantly to the strain hardening of the heterogeneous bimodal structures.In addition,the contributions of misorientation and grain size to back stress are quantitatively analyzed,and the near-linear relationship between hetero-deformation induced hardening and strain gradient is found.These findings emphasize the es-sential role of the intragranular back stress induced by strain gradient and provide an in-depth understanding of the elaborate roles of back stress in heterogeneous structures.展开更多
It is difficult to synthesize Al2O3/ZrO2 solid solution because of its low solubility under equilibrium solidification conditions.In this work,a new combustion synthesis combined with water atomization(CS-WA)method wa...It is difficult to synthesize Al2O3/ZrO2 solid solution because of its low solubility under equilibrium solidification conditions.In this work,a new combustion synthesis combined with water atomization(CS-WA)method was developed to prepare supersaturated Al2O3/ZrO2(CeO2)solid solution powders.The ultrahigh cooling rate supplied by CS-WA greatly extends solid solubility of Al2O3 in ZrO2.The precipitation mechanism of solid solution was investigated by systematic heat treatments.The initial temperature of the metastable phase decomposed into Al2O3 and ZrO2 is 1050℃,and it could be completely precipitated at 1400℃in 0.5 h.The precipitated ZrO2 particles were uniformly dispersed in Al2O3 matrix and grew into submicron scale at annealing temperature of 1450℃.Subsequently,together with detailed microstructure,phase composition,as well as mechanical properties were collaboratively outlined to discuss spark plasma sintering(SPS)behavior.The solid solution precipitated Al2O3 matrix and ZrO2 particles during the SPS process.Partial ZrO2 particles were uniformly distributed within Al2O3 matrix,while the residuary ZrO2 located at the grain boundaries and formed special transgranular/intergranular structure.The average size of nanoscale transgranular ZrO2 particles was only^11.5 nm.The compact ZrO2 toughened Al2O3 nano ceramic(N-ZTA)exhibits excellent mechanical properties.This work provides a guidance to produce nanostructured ZTA with high performance.展开更多
In order to understand the basic mechanism of intergranular cracking in pure metals during fatigue, stress-controlled push-pull fatigue tests were carried out with high purity aluminium. Tests were interrupted frequen...In order to understand the basic mechanism of intergranular cracking in pure metals during fatigue, stress-controlled push-pull fatigue tests were carried out with high purity aluminium. Tests were interrupted frequently so as to study the grain boundary (GB) cracking behaviour by the surface observation. The results show that crack initiation at GB was a process controlled by multi-factors, such as boundary structure, GB-slip interaction, GB sliding and so on. If these factors are varied so that the incompati- bility at a GB increased, the possibility of cyacking at the boundary will be raised. Some inteygranular cracking phenomena are not able to be explained by the GB stepping mechanism.展开更多
This study aims to clarify the mechanisms for the grain boundary(GB)segregation through investigating the absorption of excess solute atoms at GBs in Al−Cu alloys by using the hybrid molecular dynamics/Monte Carlo sim...This study aims to clarify the mechanisms for the grain boundary(GB)segregation through investigating the absorption of excess solute atoms at GBs in Al−Cu alloys by using the hybrid molecular dynamics/Monte Carlo simulations.Two segregation mechanisms,substitutional and interstitial mechanisms,are observed.The intergranular defects,including dislocations,steps and vacancies,and the intervals in structural units are conductive to the prevalence of interstitial mechanism.And substitutional mechanism is favored by the highly ordered twin GBs.Furthermore,the two mechanisms affect the GB structure differently.It is quantified that interstitial mechanism is less destructive to GB structure than substitutional one,and often leads to a segregation level being up to about 6 times higher than the latter.These findings contribute to atomic scale insights into the microscopic mechanisms about how solute atoms are absorbed by GB structures,and clarify the correlation among intergranular structures,segregation mechanisms and kinetics.展开更多
文摘Tensile properties, fracture characteristics and microstructures of 7055 aluminum-based alloy containing Ag after T6, T73 and RRA treatment were investigated. The results show that RRA treatment retains strength of 7055-T6 with higher electrical conductivity close to that of 7055-T73 alloy, but its elongation decreases greatly. SEM fractographs reveal that intergranular cracking and shear-type transgranular cracking are both presented on the fracture appearance of 7055-T6 specimen. After T73 treatment, the fractographs mainly consist of dimple-type transgranular cracking with minor intergranular cracking. For 7055-RRA specimen, intergranular cracking dominates with minor dimples on the fracture surface. The type and size of precipitates, width of grain boundary and the ability of precipitates to impede dislocation motion vary with heat treatment regimes. Three frature models were built on the basis of microstructural analyses.
基金supported by the National Natural Science Foundation of China(Grant Nos.52222505,52321002,and 52005185)the Natural Science Foundation of Shanghai(Grant No.23ZR1415500)+2 种基金the China Scholarship Council(Grant No.202106740014)the Innovation Program of Shanghai Municipal Education Commission(Grant No.2019-01-07-00-02-E00068)Young Elite Scientists Sponsorship Program by China Association for Science and Technology(Grant No.YESS20200029).
文摘Back stress has been proven to be the primary mechanism for superior mechanical properties of heterogeneous structures,but its quantitative contribution remains vague.The main purpose of this work is to clarify the contributions of back stress components,i.e.,intergranular residual stress and intragranular back stress,to the mechanical properties of heterogeneous structures based on the crystal plasticity theory.The results show that the intragranular back stress is smaller than the intergranular residual stress but contributes significantly to the strain hardening of the heterogeneous bimodal structures.In addition,the contributions of misorientation and grain size to back stress are quantitatively analyzed,and the near-linear relationship between hetero-deformation induced hardening and strain gradient is found.These findings emphasize the es-sential role of the intragranular back stress induced by strain gradient and provide an in-depth understanding of the elaborate roles of back stress in heterogeneous structures.
基金financially supported by the National Natural Science Foundation of China(Nos.91016014 and 51872062).
文摘It is difficult to synthesize Al2O3/ZrO2 solid solution because of its low solubility under equilibrium solidification conditions.In this work,a new combustion synthesis combined with water atomization(CS-WA)method was developed to prepare supersaturated Al2O3/ZrO2(CeO2)solid solution powders.The ultrahigh cooling rate supplied by CS-WA greatly extends solid solubility of Al2O3 in ZrO2.The precipitation mechanism of solid solution was investigated by systematic heat treatments.The initial temperature of the metastable phase decomposed into Al2O3 and ZrO2 is 1050℃,and it could be completely precipitated at 1400℃in 0.5 h.The precipitated ZrO2 particles were uniformly dispersed in Al2O3 matrix and grew into submicron scale at annealing temperature of 1450℃.Subsequently,together with detailed microstructure,phase composition,as well as mechanical properties were collaboratively outlined to discuss spark plasma sintering(SPS)behavior.The solid solution precipitated Al2O3 matrix and ZrO2 particles during the SPS process.Partial ZrO2 particles were uniformly distributed within Al2O3 matrix,while the residuary ZrO2 located at the grain boundaries and formed special transgranular/intergranular structure.The average size of nanoscale transgranular ZrO2 particles was only^11.5 nm.The compact ZrO2 toughened Al2O3 nano ceramic(N-ZTA)exhibits excellent mechanical properties.This work provides a guidance to produce nanostructured ZTA with high performance.
文摘In order to understand the basic mechanism of intergranular cracking in pure metals during fatigue, stress-controlled push-pull fatigue tests were carried out with high purity aluminium. Tests were interrupted frequently so as to study the grain boundary (GB) cracking behaviour by the surface observation. The results show that crack initiation at GB was a process controlled by multi-factors, such as boundary structure, GB-slip interaction, GB sliding and so on. If these factors are varied so that the incompati- bility at a GB increased, the possibility of cyacking at the boundary will be raised. Some inteygranular cracking phenomena are not able to be explained by the GB stepping mechanism.
基金supported by grants from the National Natural Science Foundation of China(Nos.52031017,51801237)the National Key Laboratory of Science and Technology on High-strength Structural Materials in Central South University,China(No.6142912200106).
文摘This study aims to clarify the mechanisms for the grain boundary(GB)segregation through investigating the absorption of excess solute atoms at GBs in Al−Cu alloys by using the hybrid molecular dynamics/Monte Carlo simulations.Two segregation mechanisms,substitutional and interstitial mechanisms,are observed.The intergranular defects,including dislocations,steps and vacancies,and the intervals in structural units are conductive to the prevalence of interstitial mechanism.And substitutional mechanism is favored by the highly ordered twin GBs.Furthermore,the two mechanisms affect the GB structure differently.It is quantified that interstitial mechanism is less destructive to GB structure than substitutional one,and often leads to a segregation level being up to about 6 times higher than the latter.These findings contribute to atomic scale insights into the microscopic mechanisms about how solute atoms are absorbed by GB structures,and clarify the correlation among intergranular structures,segregation mechanisms and kinetics.
