超细晶纯钛动态力学响应及变形机制

Dynamic mechanical response and deformation mechanism of ultrafine-grained pure titanium

采用分离式霍普金森压杆技术在应变速率为2000~3000 s^(-1)和温度为300~450℃条件下对超细晶纯钛进行了动态冲击实验,研究了其动态力学响应及变形机制,并利用扫描电子显微镜和透射电子显微镜对变形后的微观组织进行了表征。结果表明:超细晶纯钛的真应力-真应变曲线呈现出明显的“双应力峰”特征,随着应变速率的增加和温度的降低,其屈服强度和流变应力提高,表现出正应变速率敏感性和负温度敏感性。在应变速率为2000~3000 s^(-1)的范围内,超细晶纯钛的应变速率敏感性指数m为0.12~0.17。当应变速率大于2500 s^(-1)时,超细晶纯钛试样出现绝热剪切带,绝热剪切带产生的临界应变为0.316。在动态冲击载荷下,超细晶纯钛的变形机制由低温时的位错密度增加和位错胞形成转变为高温时的几何动态再结晶和晶粒粗化。

The dynamic impact experiments of ultrafine-grained(UFG)pure titanium were carried out with strain rate of 2000-3000 s^(-1) and temperature of 300-450℃by the split Hopkinson press bar(SHPB)technique to study dynamic mechanical response and deformation mechanism.The microstructure after deformation was characterized using scanning electron microscopy(SEM)and transmission electron microscopy(TEM).The results show that the true stress-true strain curves of UFG pure titanium show significant"double-stress peak"characteristic.The yield strength and flow stress of UFG pure titanium increase with the increase of the strain rate and the decrease of the temperature.UFG pure titanium exhibits positive strain rate sensitivity and negative temperature sensitivity.The strain rate sensitivity index m of UFG pure titanium in the range of strain rate of 2000-3000 s^(-1) is 0.12-0.17.When the strain rate is larger than 2500 s^(-1),adiabatic shear bands(ASBs)appear in the UFG pure titanium and the critical strain for the appearance of ASBs is 0.316.Under dynamic impact load,the deformation mechanisms of UFG pure titanium transform from the increase of dislocation density and the formation of dislocation cell at low temperature to geometric dynamic recrystallization and grain coarsening at high temperature.