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综述了剧烈塑性变形引起的块体纳米金属材料的结构和力学性能演变.以电化学沉积法制备的fcc结构纳米晶Ni-20%Fe(质量分数)合金为研究对象,通过对其进行不同应变量的高压扭转实验,系统分析了变形引起的结构和力学性能演变.结构表征结果表明:(1)变形引发纳米晶Ni-Fe合金晶粒旋转,实现晶粒长大.同时,晶粒长大过程伴随着位错密度、孪晶密度的演变;(2)存在一个最有利于变形孪晶生成的晶粒尺寸范围(45~100 nm),在这个晶粒尺寸范围之外,去孪晶起主导作用使原有的生长孪晶或变形孪晶消失;(3)位错密度是影响位错与孪晶反应的新的影响因素.当发生孪晶的晶粒内位错密度低时,位错可完全穿过孪晶界,部分穿过孪晶界,或被孪晶界吸收;发生孪晶的晶粒内位错密度高时,大量位错缠绕并堆积在孪晶界附近,形成应力集中,破坏孪晶界原有的共格性.为释放局部应力,将从孪晶界的另一侧发射不全位错形成层错和二次孪晶;(4)在塑性变形导致的晶粒长大过程中,原先偏聚于消失了的晶界上的C和S沿残留晶界扩散并继续偏聚于晶界上.结构与力学性能关系结果表明:随着应变量的增加,应变强化、应变软化交替出现.位错密度对硬度的演变起主导作用,其它结构演变(如孪晶密度的变化和晶粒尺寸变化)对硬度的演变起次要作用.
In this paper, the structural and mechanical properties of bulk nanocrystalline materials caused by drastic plastic deformation are reviewed.The fcc nanocrystalline Ni-20% Fe (mass fraction) alloy prepared by electrochemical deposition is studied, The experimental results show that: (1) The deformation causes the grains of nanocrystalline Ni-Fe alloy to rotate and realize the grain growth. At the same time, the grain growth The process is accompanied by the evolution of dislocation density and twin density. (2) There is a grain size range (45 ~ 100 nm) that is most favorable to the formation of deformation twins. Outside this grain size range, (3) The dislocation density is the new influence factor of the dislocation and twinning reaction. When the dislocation density of twin in the grain is low, the dislocation density The fault may completely penetrate the twin boundaries, partially through the twin boundaries, or be absorbed by the twin boundaries. When the twin dislocations have a high density of dislocations, a large number of dislocations are wound and deposited near the twin boundaries, forming stress Concentrate, destroy the twin coexistence of the original boundaries. To release the local stress will be from (4) In the process of grain growth due to plastic deformation, the C and S residues originally segregated on the disappeared grain boundary remain in the residual The grain boundary diffuses and continues to segregate on the grain boundaries.The results of the relationship between structure and mechanical properties show that strain hardening and strain softening alternate with the increase of strain amount.The dislocation density plays a leading role in the evolution of hardness and the evolution of other structures Such as twin density changes and grain size changes) have a secondary effect on the evolution of hardness.