纳米面心立方金属的变形机制及影响其力学性能的因素

综述了纳米面心立方金属的变形机制随晶粒尺寸的减小而发生的变化,即变形机制由晶界处发射不全位错、形成孪晶转变为晶界滑移、晶粒转动.当变形机制为晶界处发射不全位错、形成孪晶时,存在最佳孪晶形成晶粒尺寸范围,此时的孪晶形核应力最小.另一方面,随着晶粒尺寸的减小,在变形机制发生转变的临界晶粒尺寸附近存在韧-脆断裂方式的转变.提高孪晶密度、在纳米晶材料中加入微米晶相形成双峰晶粒材料可以提高纳米晶材料的塑性,得到更好的综合机械性能.

Deformation Mechanism and Dependent Factors of the Mechanical Properties of Face-centered-cubic Nano-crystalline Metals

As the grain sizes are decreased, the transition of deformation mechanism from emission from grain boundaries and twinning to grain boundary partial dislocation sliding and grain rotation in face-centeredcubic nano-crystalline metals is summarized. There is a optimum twinning grain size range with minimum critical stress for twin nucleation when partial dislocations emit from grain boundaries and twinning is the main deformation mechanism. Below the critical grain size with lower value than one of the optimum grain size range, the fracture mechanism changes from ductile to brittle one. Improvement of the ductility of the nano - crystalline metals can be obtained by increasing the twinning densities or synthesizing materials with bimodal grain size.