Microstructural Evolution Behavior of Adiabatic Shear Bands Induced by High-speed Projectile Impact in TC32 Titanium Alloy

The microstructure characterization and evolution behavior of TC32 titanium alloy after high-speed projectile impact were studied by optical microscope (OM), scanning electron microscope (SEM) and transmission electron microscopy (TEM). The distribution of adiabatic shear band (ASB) and stress around the crater has always been a semi-circular diffusion. The rotating refinement process of large equiaxed grains and elongated lath subgrains in adiabatic shear band is observed. Focus ion beam (FIB) technology was used to accurately prepare TEM samples from the crack tip in the ASB. The coexistence of the amorphous regions, the amorphous-to-crystalline transition regions, the fine-scale nano-crystalline region around the crack tip is found. The calculation proves that the temperature rise in ASB could cause microstructure melting, the amorphous regions and small size nanocrystals form after fast quenching. Because the microstructure in the ASBs is fine equiaxed grains and amorphous with higher strength, the area between the deformed band and matrix is relatively weakened, and it is found that the initiation of cracks in adiabatic shear bands is mainly concentrated at the junction of deformed band and matrix, and the crack propagates in the form of microvoids rotation coupling.