Twinnability of Ti-V Binary Alloys: Simulation and Experiment

^a Shanghai Key Lab of Advanced High-temperature Materials and Precision Forming, Shanghai Jiao Tong University, Shanghai 200240, China.
^b State Key Laboratory of Performance Ceramics and Superfine Microstructure, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 201899, China

^* jhuang@mail.sic.ac.cn, apdong@sjtu.edu.cn

Abstract

Recently metastable β titanium alloys has attracted much attention due to their important application in biomaterials. In this study, the defects and mechanical properties of bcc disordered β Ti-alloys are investigated theoretically by first-principles method. The elastic moduli, generalized stacking fault energies, twinnability in β Ti-V alloys were surveyed by calculations with virtual crystal approximation. The results show that the structural stability and generalized stacking fault energy decrease with reducing valence electron number (e/a) in the β Titanium alloys. Both twinning formation energies and twinning migration energies decrease with reducing electron valance numbers, which suggests that the energy barrier for twinning formation deceases with lower structural stability. The twins in the metastable Ti-25 at.%V alloy can form near the crack tip or triggered by the high local stress during the nucleation. As the twin is thickened, the required local stress is also greatly reduced and it can grow away from the crack tip for metastable titanium alloys. Transmission electron microscopy (TEM) shows that twins are more easily observed in Ti-V alloys with relatively low electron concentrations, which confirms the theoretical conclusion that the lower the electron concentration, the easier the twin formation.