Dynamic compression deformation behavior of laser directed energy deposited α + β duplex titanium alloy with basket-weave morphology

Abstract

Duplex titanium alloy with basket-weave morphology made by laser directed energy deposition (LDED) technique, has a bright application prospect in the armor protection field attributed to its excellent specific strength and bulletproof performance. In this research, the dynamic compressive deformation mechanisms of LDEDed TC11 titanium alloy under a strain rate of 3000/s are systematically investigated by investigating the dislocation slipping and twinning behavior. Meanwhile, this work gives explanations of the microstructure evolution of subsequent heterogeneous shear localization. The results indicate that TC11 alloy with basket-weave morphology possesses huge improvement in the average dynamic flow stress, uniform plastic strain, and impact absorption energy in contrast to that of titanium alloys with an equiaxed microstructure, which is known as the optimum prepared via traditional forming methods. The loading direction to α laths is largely responsible for slip modes manifestation under dynamic compression, which is illustrated in the unit triangle. When loading along < 0001 > at the vertex of the unit triangle, both basal slip and prismatic slip systems could not be motivated. When loading along directions within the unit triangle, either or both basal slip and prismatic slip systems could be activated, causing α lath twisting, rotation, or even refinement. Meanwhile, the Schmid factors reduction caused by α laths rotation results in the twinning, which will reduce the slip mean free path. During the heterogeneous shear localization, the adiabatic shear bands (ASB) formation finally leads to shear failure. The α laths within the transition zone in ASB are compressed to less than 200 nm in thickness. Ultrafine nanoscale equiaxed grains with few defects in the center zone of ASB are generated under dislocations pile-up and sub-grain rotation.