Deformation localization and recrystallization in TC4 alloy under impact condition

GCr15 steel balls 4 mm in diameter were used as projectiles to impact different thickness Ti-6Al-4V targets at a speed of 1.5 km/s. Two types of adiabatic shear bands (ASBs) near the craters were distinguished by optical microscopy deformed shear bands; white-etching shear bands. The white-etching bands and deformed bands coexist in thin targets. In two other types of targets, only the white-etching bands were observed. The boundary between the white-etching bands and matrix is very clear. Micro-voids and cracks are observed in white-etching bands. Observation by transmission electron microscope (TEM) reveals that the white-etching bands contain nano-size equiaxed grains, which confirm that recrystallization occurs during white-etching bands formation.