The mechanical size effect of nanostructured,dual-phase CrCoNi medium-entropy alloy(MEA)was investigated by combining in-situ micro-compression testing with post-mortem electron microscopy analysis.The alloy possesses...The mechanical size effect of nanostructured,dual-phase CrCoNi medium-entropy alloy(MEA)was investigated by combining in-situ micro-compression testing with post-mortem electron microscopy analysis.The alloy possesses a superior yield strength up to~4 GPa,primarily due to its hierarchical microstructure including column nanograins,preferred orientation,a high density of planar defects and the presence of the hexagonal close packed(HCP)phase.While the yield strength of the alloy has shown sizeindependency,the deformation behaviour was strongly dependent on the sample size.Specifically,with decreasing the pillar diameters,the dominant deformation mode changed from highly localized and catastrophic shear banding to apparently homogeneous deformation with appreciable plasticity.This transition is believed to be governed by the sizedependent critical stress required for a shear band traversing the pillar and mediated by the competition between shearinduced softening and subsequent hardening mechanisms.In addition,an unexpected phase transformation from HCP to face-centered cubic(FCC)was observed in the highly localized deformation zones,leading to strain softening that contributed to accommodating plasticity.These findings provide insights into the criticality of sample dimensions in influencing mechanical behaviors of nanostructured metallic materials used for nanoelectromechanical systems.展开更多
The influence of specimen size on the mechanical behavior of Au pillars is studied by means of molecular dynamics (MD) simulations with the EAM potential.Under compression at 300 K,as the deformation of pillars is in ...The influence of specimen size on the mechanical behavior of Au pillars is studied by means of molecular dynamics (MD) simulations with the EAM potential.Under compression at 300 K,as the deformation of pillars is in the plastic stage,nucleation of partial dislocations is observed.The coupling effect of surface stress and thermal activation is considered when analyzing the size effect on the yield property of the Au pillars.It appears that both the tensile stress component and the temperature in the surface layer impart significant effect on the mechanical behaviors of the nano-sized Au pillars.展开更多
Molecular dynamics simulations using embedded atom method (EAM) potential were performed to study nano-void growth and coalescence at grain boundary in face-centered cubic bicrystal copper. Thin-plate specimens subjec...Molecular dynamics simulations using embedded atom method (EAM) potential were performed to study nano-void growth and coalescence at grain boundary in face-centered cubic bicrystal copper. Thin-plate specimens subjected to uniaxial tension strain with one-void and two-void at the centered grain boundary were employed to analyze the effect of specimen size, temperature and applied strain rate on the stress-strain response, incipient yield strength and macroscopic effective Young's modulus. The evolutions of dislocations, twin bands and void shapes under different specimen sizes were also presented. The obtained results show that, regardless of the void numbers, the specimen sizes, temperature, the applied strain rate had significant influence on the void shape evolution, stress-strain curve and incipient yield strength, while negligible effects on the macroscopic effective Young's modulus except for the temperature. Moreover, the voids growth rate along the grain boundary was also found to be associated with the specimen sizes.展开更多
基金supported by the Australian Research Council Discovery Projects Grantpartly supported by the Fundamental Research Funds for the Central Universities(SWU118105)+1 种基金the financial support from Australia Research Council(DE170100053)the Robinson Fellowship Scheme of the University of Sydney(G200726)。
文摘The mechanical size effect of nanostructured,dual-phase CrCoNi medium-entropy alloy(MEA)was investigated by combining in-situ micro-compression testing with post-mortem electron microscopy analysis.The alloy possesses a superior yield strength up to~4 GPa,primarily due to its hierarchical microstructure including column nanograins,preferred orientation,a high density of planar defects and the presence of the hexagonal close packed(HCP)phase.While the yield strength of the alloy has shown sizeindependency,the deformation behaviour was strongly dependent on the sample size.Specifically,with decreasing the pillar diameters,the dominant deformation mode changed from highly localized and catastrophic shear banding to apparently homogeneous deformation with appreciable plasticity.This transition is believed to be governed by the sizedependent critical stress required for a shear band traversing the pillar and mediated by the competition between shearinduced softening and subsequent hardening mechanisms.In addition,an unexpected phase transformation from HCP to face-centered cubic(FCC)was observed in the highly localized deformation zones,leading to strain softening that contributed to accommodating plasticity.These findings provide insights into the criticality of sample dimensions in influencing mechanical behaviors of nanostructured metallic materials used for nanoelectromechanical systems.
基金supported by the National Natural Science Foundation of China (Grant Nos.10872197,11021262,11172303,11132011)
文摘The influence of specimen size on the mechanical behavior of Au pillars is studied by means of molecular dynamics (MD) simulations with the EAM potential.Under compression at 300 K,as the deformation of pillars is in the plastic stage,nucleation of partial dislocations is observed.The coupling effect of surface stress and thermal activation is considered when analyzing the size effect on the yield property of the Au pillars.It appears that both the tensile stress component and the temperature in the surface layer impart significant effect on the mechanical behaviors of the nano-sized Au pillars.
基金supported by the Open Foundation of State Key Laboratory of Explosion Science and Technology, Beijing Institute of Technology (Grant No. KFJJ11-0Y)the National Basic Research Program of China (Grant No. 2010CB631005)the National Natural Science Foundation of China (Grant Nos. 11172148 and 51071094)
文摘Molecular dynamics simulations using embedded atom method (EAM) potential were performed to study nano-void growth and coalescence at grain boundary in face-centered cubic bicrystal copper. Thin-plate specimens subjected to uniaxial tension strain with one-void and two-void at the centered grain boundary were employed to analyze the effect of specimen size, temperature and applied strain rate on the stress-strain response, incipient yield strength and macroscopic effective Young's modulus. The evolutions of dislocations, twin bands and void shapes under different specimen sizes were also presented. The obtained results show that, regardless of the void numbers, the specimen sizes, temperature, the applied strain rate had significant influence on the void shape evolution, stress-strain curve and incipient yield strength, while negligible effects on the macroscopic effective Young's modulus except for the temperature. Moreover, the voids growth rate along the grain boundary was also found to be associated with the specimen sizes.
