透射电镜原位拉伸研究金属材料形变机制

In situ TEM/HRTEM investigations on deformation mechanisms in metals

透射电镜原位拉伸方法是研究材料形变机制的一种直观而有效的手段。将拉伸实验与高分辨透射电镜相结合,通过在原子尺度上直接观察,实时地记录应力应变作用下晶体材料微观结构的演变及位错的产生和运动等,直观地揭示材料在弹性及塑性阶段的形变机理。本文将重点回顾近年来作者用透射电镜原位拉伸方法在研究金属材料形变机制方面的工作进展。主要包括纳米金属材料的晶界发射和吸收不全位错、晶粒旋转长大等变形机制,及金属材料在变形过程中的几种可逆形变机制。

Direct and dynamic atomic level imaging during tensile straining inside a transmission electron microscope（TEM） provides an insight into the deformation processes,which could not be discovered properly by postmortem or ex situ TEM observations.Therefore,in situ TEM observations are of advantage to study the reversible deformation behaviors.Using a combination of in situ tensile straining and high-resolution transmission electron microscopy（HRTEM）,the microstructure evolution as well as the nucleation and movement of dislocations upon tensile strain can be recorded in real time and at atomic scale.Based on the intuitive and dynamic observations,the deformation mechanisms in both the elastic and plastic portions could be explored.In this paper,we reviewed several new deformation mechanisms in metallic materials discovered by in situ TEM /HRTEM.A high propensity for the reversibility of the stacking fault was found in nanocrystalline Ni.With the in situ atomic-scale observation,the evidences of the partial dislocation emission from a GB and the absorption of the partial by the original GB were captured.Deformation-induced grain rotation and growth as one of plastic deformation mechanisms in nc materials was revealed by exhibiting the complete process of individual grain rotation and neighboring grain rotation/growth.Reversible deformation twinning was successfully observed in pure,coarse-grained aluminium.By capturing the dynamical process of the twinning and de-twinning at the atomic scale,the physics of the reversible twinning has been revealed.For the abnormal nonlinear elastic deformation behavior of a beta-titanium alloy,HRTEM observations during in situ tensile test revealed new reversible deformation mechanisms：reversible nanodisturbances and reversible movement of homogenously nucleated dislocations.