Investigation on the spallation properties and failure mechanism of selective laser melted Ti-6Al-4V alloy with heat treatment under shock load

Abstract

In this study, the effect of heat treatment on the microstructure of selective laser-melted Ti-6Al-4V alloy and the corresponding spalling performances and damage mechanism at ultra-high-speed (UHS) of 730 m/s are studied. Results show that the acicular martensite in the as-built sample is transformed into large grain basket-weave and Widmanstatten structures with solution treatment at 950 ℃ and 1050 ℃, respectively. The spallation damage mechanism is characterized by the aspects of grain refinement ratio (GRR) and damage porosity (DP). The HT-1050 sample has the highest GRR and DP, while the HT-950 sample has the lowest values, indicating that the HT-950 sample has the highest resistance of spallation. Due to the difference in microstructure morphology and grain size of the three samples, the spalling damage mode of the original sample is characterized by brittle fracture, and then it changes to pore growth and coalescence after heat treatment, larger grains have strong guiding effects on the coalescence of pores. The coalescence of the pores is always accompanied by dynamic recrystallization, thus reducing the local dislocation density and optimizing the development path of cracks. Based on the above work, can provide theoretical support for promoting the application of additive manufacturing alloys in defense industry and aerospace fields.