Effect of Single and Duplex Stage Heat Treatment on the Microstructure and Mechanical Properties of Cast Ti–6Al–4V Alloy

Abstract

The effect of single and duplex stage heat treatment on the microstructure and mechanical properties of cast Ti–6Al–4V alloy was studied. The single stage heat treatment (SSHT) involved solution annealing at 935 °C for 10 min followed by water quenching, while the duplex stage heat treatment (DSHT) involved solution annealing at 935 °C for 10 min, furnace cooling to 600 and 700 °C, followed by isothermal holding for 30 min and subsequent water quenching. The properties characterization was conducted using microstructure investigation along with tensile, hardness, and Charpy impact tests. The impact fracture surfaces were observed using Scanning Electron Microscope. After SSHT, an increase in the tensile strength and hardness at the expense of the tensile elongation and impact toughness was recorded as compared with the as-cast alloy. This is attributed to the formation of a brittle α′ martensite phase in the microstructure after quenching from 935 °C. On the other hand, DSHT enhances the percent elongation and impact toughness over the as-cast alloy and SSHT. The formation of α′ martensite-free microstructure as well as controlling the composition of the different microstructural constituents during DSHT optimizes the mechanical properties.