高锰TWIP钢中形变孪晶界缺陷的电镜表征研究

Electron microscopy characterization of the defects of deformation twin boundaries in high manganese TWIP steels

通常认为孪晶界是完全共格和无缺陷的,但变形过程中产生的孪晶界往往带有很多缺陷。本文通过高分辨透射电镜观察研究了高锰孪生诱发塑性(twinning induced plasticity,TWIP)钢中形变孪晶界的缺陷特征。结果表明,高锰TWIP钢中形变孪晶界的缺陷包括界面原子台阶、9R结构单元和由于位错和孪晶界相互作用产生的高密度位错。与传统认为9R结构由Σ3{112}非共格孪晶界的分解产生不同,形变孪晶界上9R结构单元由晶界直接发射不全位错形成。位错和孪晶界的交互作用造成了孪晶的退化,并在孪晶界附近产生了大量位错,包括高密度的全位错和Frank分位错。基于形变孪晶界缺陷的电镜表征,分析和总结了高锰TWIP钢的强韧化机制。

Twin boundaries(TBs)are usually considered to be coherent and perfect.Here we report that deformation twins in twinning induced plasticity(TWIP)steels are often defective with steps,9R structures and massive dislocations formed by the dislocation-TB interactions.These imperfections are finely identified by high-resolution transmission electron microscopy(HRTEM).It is found that some 9R structures can be directly produced by the glide of Shockley partial dislocations(SPDs)emitted from boundaries,which differs from the traditional 9R phase created by the dissociation ofΣ3{112}incoherent TB.Dislocation-TB interactions result in de-twinning at the both sides of the primary deformation twin and produce different types of dislocations near the TBs,including high densities of full dislocations and the Frank partial dislocation.Base on the analysis of various defects at TBs,the mechanism of twinning-induced plasticity and strain hardening is summarized in TWIP steels.