剪切应力对Ti-6Al-4V合金α相形核及微织构形成的影响

The influences of applied shear stress on nucleation and micro-texture formation of α phase in Ti-6Al-4V

摘要:

采用相场动力学方法模拟Ti-6Al-4V合金中b→α转变过程，研究钛合金中不同方向的外加剪切应力对α析出相变体形核及微织构形成的影响。模型输入数据来自Pandat热力学与动力学数据库及JmatPro (TTT-Ti)。选取x[101]-y[12-1]-z[-111]坐标系，保持时效温度不变，分别沿(101)[-111]β或(12-1)[-111]β施加不同大小(10, 30及50 MPa)的正反向切应力，考察剪切加载对合金微观组织演化的影响。结果表明：过冷度一定时，随剪切应力增大，析出变体与剪切应力之间的弹性相互作用在相变过程中逐渐起主要作用，对α相变体的选择作用逐渐增强；应力大小一定时，切应力对变体选择的作用强于正应力；沿(101)[-111]β或(12-1)[-111]β方向外加剪切应力，正向切应力分别促进两种与一种α变体的选择，而反向切应力均主要选择一种α变体。因而在b向α转变过程中，切应力更有利于α相微织构的形成。

Abstract:

To investigate the influences of applied shear stress on the nucleation process and micro-texture formation of α precipitates, β→α transformation in Ti-6Al-4V alloy was simulated by phase field method using Pandat software and JmatPro (TTT-Ti) databases as direct input in the model. The effects of applied positive and negative shear stresses (10, 30 and 50 MPa) along (101)[-111]β or (12-1)[-111]β on the microstructure evolution of Ti-6Al-4V alloy were explored under aging at certain temperature. The results show that. with the increase of shear stress, the elastic interaction between applied stress and α variants gradually plays more significant role in determining the microstructure of the system under certain undercooling, t herefore, the selection of α variants is gradually enhanced. It was found that the shear stress has a stronger effect on the variant selection than that of normal stress, therefore maybe more effective on microtexture formation. With the increase of shear stress, two or one type of variant are selected under positive shear, and one type of variant is favored by the negative shear along (101)[-111]β or (12-1)[-111]β respectively.