Effect of grain size on the shock-induced response and spall fracture behavior of a metastable β titanium alloy subjected to repeated impact

The dynamic failure behavior of titanium alloys has received increasing attention due to their promising application in high-strain-rate service environments. In this research, a series of plate impact experiments were carried out on a metastable β titanium alloy Ti–2Al-9.2Mo–2Fe (2A2F) to reveal the influences of multiple shock and β grain size on its spall fracture behavior. The results show that the spall behavior of 2A2F is significantly dependent on the number of impacts and β grain size. For the alloy with a small grain size, after first shocked at 6 and 12 GPa, the spall strength is increased by more than 60% during the second shock loading process. However, the pre-shock process has little effect on the spall strength of the alloy with the larger grain size. The microstructure analyses show that dislocation proliferation and β-to-α″/ω phase transformations occurred during the shock pulse. The α″ variants and fishbone-like α″ structures were also formed in 2A2F at the higher shock stress. These shock-induced substructures strengthen the β grains, leading to the shift in the nucleation site and propagation path of the spall micro-damages and the improvement of the spall strength.