微纳米晶金属的应变率敏感性及应变硬化行为分析

基于亚微米、纳米晶粒组织塑性变形过程中多种变形机制(位错机制、扩散机制及晶界滑动机制)共存,建立了理论模型,用于定量研究亚微米、纳米晶粒组织的塑性变形行为.以铜为模型材料,计算分析了晶粒尺度、应变率以及温度对亚微米、纳米晶粒组织塑性变形行为的影响.结果表明:相比粗晶铜,亚微米晶铜表现出明显的应变率敏感性,并且应变率敏感系数随晶粒尺度及变形速率的减小而增大;同时,增大变形速率或降低变形温度都能提高材料的应变硬化能力,延缓颈缩发生,进而提高材料的延性.计算分析结果与实验报道吻合.

ANALYSIS OF STRAIN RATE SENSITIVITY AND STRAIN HARDEING BEHAVIOR IN ULTRAFINE-GRAINED AND NANOCRYSTALLINE METALS

A physically based model is proposed to describe the plastic deformation of ultrafine grained and nanocrystalline metals.In the framework of the model,three mechanisms of plastic deformation,namely dislocation glide mechanism,diffusion mechanism and grain boundary sliding mechanism were considered to account for the plastic deformation behavior.Based on the model,we used copper as a "prototype" material to investigate the effects of grain size,strain rate and temperature on the plastic deformation behavior.The calculated results show that the strain rate sensitivity increases with decreasing grain size or strain rate,while the flow stress increases with increasing strain rate or decreasing temperature.In addition,increasing strain rate can improve the ductility of the ultrafine grained Cu.The calculation results are in good agreement with experiments in literature.