一种亚稳型β钛合金在高应变率下的多种变形机制

Multiple deformation mechanisms of a metastable β Ti-V alloy at high strain rates

摘要:

本文以二元Ti-16V合金为研究对象，着重研究其动态压缩性能与变形机理。其中，动态压缩实验在霍普金森压杆装置上进行。对于亚稳型Ti-16V合金而言，其流变抗力与应变硬化速率随加载应变率(1000~3700 s-1)的变化并不十分显著。根据变形试样金相组织的演变规律可以判定材料的临界失稳应变率约为3000 s-1。采用电子背散射衍射技术与透射电子显微镜技术可以确定Ti-16V合金动态压缩的主要变形机制为{332}<113>型孪生与应力诱发ω相变。借助本文中构建的球形坐标系可以计算BCC孪生的Schmid因子并对Ti-16V合金的动态孪生行为加以分析，最后证明临界Schmid因子是决定孪生开动与否的重要参数，并且结合临界Schmid因子与正应力值可以计算得出Ti-16V合金在动态压缩条件下形成的{332}<113>型孪晶的临界分切应力约为334~338 MPa。

Abstract:

In the present work, compressive properties and deformation modes of binary Ti-16V alloy have been investigated during dynamic compressive tests performed on split Hopkinson pressure bar. For metastable Ti-16V alloy, the flow stress and strain hardening rate were both independent of the loading strain rate within the strain rate range (1000~3700 s-1) in our experiments. According to the optical microstructure evolution, the critical instability strain rate was confirmed to be about 3000 s-1. Multiple deformation modes including {332}<113> type mechanical twinning and stress induced ω phase transformation were identified by electron backscatter diffraction and transmission electron microscopy. With the help of Schmid factor values calculated in a spherical coordinate system, the dynamic twinning behavior of Ti-16V alloy was analyzed and the critical Schmid factor was proved to be a key parameter determining the activation of twinning behavior. Combining the critical Schmid factor value and true stress, the critical resolved shear stress range of {332}<113> type twinning was calculated to be 334~338 MPa.