Effect of transus based heat treatment on material characterisation of wrought and additive titanium alloy Ti-6Al-4 V

Abstract

Titanium alloy, Ti-6Al-4 V is a popular titanium alloy used in industries such as Biomedical, Aerospace, and Automotive [1]. This is due to its superior mechanical properties such as high tensile strength, corrosion resistance and fracture toughness [2]. The main objective of this research project is to provide insights about the effect of transus based heat treatment on microstructure and mechanical properties of wrought and SLM Ti-6Al-4 V. Selective Laser Melting (SLM) which is a Direct Metal Laser Melting (DMLM) process is used to print samples in this research. Three temperature points near to alpha beta transus zone were selected to determine the effect of heat treatment on the material characterisation. The experimental design consists of heat treating, wrought and SLM Ti-6Al-4 V samples to the selected temperatures, 750 °C, 800 °C and 900 °C and followed up with furnace cooling. Further, the heat-treated samples are subjected to metallographic examination, microhardness testing and phase quantification using EBSD. An analysis of changes in microstructure will be conducted to provide a relationship between the effect of heat treatment and the changes in microstructure and corresponding microhardness. Wrought and SLM titanium samples heat treated at 900 °C. show maximum transformation to alpha phase against overall phase composition at 92% and 83% respectively. The bulk hardness analysis using Vickers concludes that the wrought sample heat treated at 900 °C. and SLM as build sample have almost a similar hardness level at 414 Hv and 407 Hv respectively. The paper concludes that heat treatment effect on SLM microstructure leads to gradual decomposition of martensitic alpha whereas accumulation of alpha into a globular alpha is observed in a wrought sample.