Deformation and fracture mechanism of Ti-6Al-4V target at high and hyper velocity impact

•In this paper, the microstructure changes of craters of TC4 target at three impact velocities are studied in detail. Three types of twins formed in the craters are analyzed, two types of dynamic recrystallization in the craters are distinguished, and three different adiabatic shear bands in the craters are observed and classified. The difference of crater damage mechanism between high velocity and hypervelocity impact is summarized. This paper studies the deformation and fracture mechanism of Ti-6Al-4V titanium under high velocity (970 m/s and 1590 m/s) and hypervelocity (2240 m/s) impacts. For the Ti-6Al-4V target, as the impact velocity increases, the volume of the crater increases, and the shape of the crater gradually changes from a shallow dish shape to a hemispherical shape. After impact at 970 m/s, dislocation slip and twining occur in the crater, forming a large number of dislocation cells and {10-12} tensile twins; several adiabatic shear bands (ASBs) are formed in the crater, and the grains inside the ASBs are severely elongated with few microvoids. After impact at 1590 m/s, the overall deformation degree of the crater increases, in addition, {11-22} compression twins are formed in some deformed grains and recrystallization occurs in some ASBs. When the impact velocity reaches hypervelocity (2240 m/s), in addition to the deformation characteristic above, FCC twins and martensitic transformation also occur in the crater, and the number of ASBs increases significantly, many microvoids are generated and connected to form macrocracks in ASBs; meanwhile, a few spallation cracks are also formed in the crater. The calculation results show that the recrystallization mechanism in the ASB is subgrain rotational dynamic recrystallization.