动态加载时β钛合金马氏体相变研究

为了研究应变速率对β钛合金马氏体相变的影响, 采用分离式霍普金森压杆对Ti-5Al-5Mo-5V-1Cr-1Fe β钛合金进行了不同应变速率下(400~1 600 s^-1)的动态变形, 采用光学显微镜、电子背散射衍射和透射电镜研究了动态变形后的微观组织。结果表明, 提高冲击功和应变速率可以提高Ti-5Al-5Mo-5V-1Cr-1Fe β钛合金的屈服强度, 当应变速率为1 600 s^-1时, 屈服强度可达1 250 MPa。在动态冲击过程中, β晶粒中出现大量板条状α'马氏体, 马氏体的面积分数随应变速率的增加而增大, 说明应变速率对β钛合金的马氏体相变起着重要作用。应变速率会加速马氏体相变, 是因为随着应变速率增加, 马氏体的形核位置更多, 马氏体形成的吉布斯自由能降低。

Martensitic Transformation of β Titanium Alloy Under Dynamic Loading

In order to study the effect of strain rate on martensitic transformation of β titanium alloy, the dynamic deformation of a Ti-5Al-5Mo-5V-1Cr-1Fe β-titanium alloy at different strain rates (400~1 600 s^-1) was carried out by using split Hopkinson pressure bar (SPHB). Then, the microstructure after dynamic deformation was studied by using optical microscope, electron backscatter diffraction and transmission electron microscope. The results show that the yield strength of Ti-5Al-5Mo-5V-1Cr-1Fe β titanium alloy can be increased by increasing the impact energy and strain rate. With the strain rate at 1 600 s^-1, the yield strength can reach 1 250 MPa. During the dynamic impact process, a large amount of lath-shaped α'-martensite appeared in the β grains, and the area fraction of martensite increases with the increase of the strain rate, indicating that the strain rate plays an important role in the martensite transformation of the β titanium alloy. The strain rate can accelerate the martensite transformation, because as the strain rate increases, there are more nucleation sites for martensitic transformation and the Gibbs free energy for the formation of martensite decreases.