液氮温度下纯Ti动态塑性变形中的孪晶变体选择

Selection of Twin Variants in Dynamic Plastic Deformation of Pure Ti at Liquid Nitrogen Temperature

在液氮温度下对商用纯Ti进行了动态塑性变形(DPD),利用电子背散射衍射(EBSD)技术观察变形前后微观组织的变化,分析孪生对变形前后Schmid因子(m)的影响,提出一种多晶纯Ti孪晶变体的选择机制。结果表明,经过液氮温度DPD后,纯Ti中出现高密度初级孪晶,并伴有二级孪晶和双孪晶;孪晶形成后,基面滑移的m发生明显改变,大量晶粒的m靠近0.5;在原有滑移和孪生匹配关系的几何相容因子(m')和相邻晶粒的Schmid因子(m1)基础上提出了新的参数取向相容因子ω(ω=m_(1)·m')作为孪晶变体的选择依据,并定量分析了多晶纯Ti塑性变形过程中的孪晶变体。发现ω决定了多晶纯Ti孪晶变体的选择,同时发现相邻晶粒锥面滑移在促进孪晶变体启动中起主要作用。

Pure Ti can form twins during deformation due to the hcp crystal structure,and some kinds of twins can easily form under certain conditions,thus affecting the properties of materials.It has considerable influence on the properties of materials through the regulation of twin types and variants.This work investigates the effect of the dislocation slip of adjacent grains on the selection of twin variants during the deformation of pure Ti.The dynamic plastic deformation(DPD)of commercially pure Ti(99.9%)was performed at liquid nitrogen temperature(-196℃).The microstructure before and after the deformation was observed using EBSD.The influence of twinning on Schmid factor(m)before and after deformation was investigated,and a mechanism for selecting twin variants of polycrystalline pure Ti was proposed.The results show that after DPD at liquid nitrogen temperature,high-density primary twins appeared in pure Ti,followed by secondary and double twins.After twinning,the Schmid factor of basal slip changed noticeably,and the m of a large number of grains was close to 0.5.Based on the geometric compatibility factor(m')of the original slip and twin matching relationship and the Schmid factor of an adjacent grain(m_(1)),a new orientation compatibility factorω(ω=m_(1)·m')was established,and the selection of twin variants in the plastic deformation of polycrystalline pure titanium was quantitatively analyzed.It was discovered that theωdetermines the selection of twin variants in pure Ti,and the pyramidal slipof the adjacent grain plays a significant role in promoting the initiation of twin variants.