TC18钛合金绝热剪切带晶粒细化机制

Refining Mechanisms of Grains in the Adiabatic Shear Band of TC18 Titanium Alloy

采用分离式霍普金森压杆,对TC18钛合金试样进行室温高应变率(103s-1)剪切试验,通过光学显微镜、扫描电镜及透射电镜观察绝热剪切带微结构,研究高应变率变形条件下TC18钛合金中所形成绝热剪切带的晶粒细化机制。TEM观察表明:绝热剪切带中晶粒细化是由3种机制共同作用的结果。第1种机制是由于变形晶粒中位错快速增殖、快速运动、塞积,塞积处产生巨大应力集中,导致形成裂纹并最终断裂形成细小晶粒;第2种机制为本研究提出的细小晶粒由拉长晶粒的"内颈缩"方式形成;第3种机制——细小晶粒由动态再结晶形成。

Dynamic shearing experiment on TC18 titanium alloy was carried out by using a split Hopkinson bar process.Refining mechanism of grains in the adiabatic shear band of TC18 titanium alloy deformed under the conditions of high strain-rate were investigated by means of OM,SEM and TEM.The results of TEM observation show that the grains in the adiabatic shear band of TC18 titanium alloy are refined due to the combined action of three mechanisms.The first mechanism is that dislocations were rapidly reproduced,moved and clogged at the obstacles such as grain boundary,second-phase particles,and so on;then,cracks were generated in the head of clogging of dislocation due to huge stress resulted from the clogging of dislocation;finally,smaller grains were formed due to breakdown of elongation grain.The second refining mechanism of grains,which is presented by us first,is inner-necking mode.The third one is dynamic recrystallization.