Effect of cycling heat treatment on the microstructure,phase,and compression behaviour of directed energy deposited Ti-Mo alloys

In this study,the effect of triple-cycling heat treatment on the microstructure,phase,and compression behaviour of directed energy deposited(DED)Ti-7Mo alloy was investigated with a focus on a non-equilibrium to equilibrium microstructure transition.As a result of thermal accumulation,in situ cycling,and rapid solidification,the as-deposited sample presents a continuous gradient microstructure withα-Ti in the top region andα+βin the bottom region.After the triple-cycling heat treatment,theα+βTi at the bottom region,which is non-equilibrium,changes to a state of equilibrium nearα-Ti.Meanwhile,the microstructure becomes more uniform throughout the entire sample.The morphology of theα-Ti phase changes from acicular to a short rode-like shape with increases in the number of dimensions.In terms of the mechanical properties,both the microhardness and compression properties were improved,particularly with respect to the fracture characteristics.The heat-treated sample possesses a much higher ductility than the brittle fractural behaviour.This work provides new insights into the microstructure and property optimisation and homogenisation of DED-processed Ti-based components with cycling heat treatment.