Impact of Heat Treatment on Microstructure and Mechanical Characteristics of Laser Powder Bed Fused Ti-6Al-4V Alloy: A Comprehensive Investigation

Abstract

The use of post heat treatment is essential in order to enhance the microstructure of additively produced Ti-6Al-4 V to meet the specific requirements set out by the aerospace and automotive sector. Nevertheless, the comprehensive understanding of the correlation between the distinctive microstructural characteristics resulting from heat treatment and the associated mechanical characteristics of Ti-6Al-4 V (Grade 23) produced using laser powder bed fusion (LPBF) technique remains insufficient. The present research work systematically examines the impact of annealing heat treatments (HT) on the microstructural changes and resulting mechanical characteristics of top, side and basal surface of Ti-6Al-4 V (Grade 23) alloy processed through LPBF method. The microstructure was characterized using optical microscopy (OM) and scanning electron microscopy (SEM). The observed microstructure of the as-deposited sample characterized by a coarse lamellar, needle-like and complicated basketweave structures consisting of α + α′ phases. The complex-shaped needle-like α + α′ structures, rod and particle-shaped structure with β phase was observed in HT sample. Elemental analysis of microstructure was performed using energy-dispersive x-ray spectroscopy (EDS). In addition to inducing phase change, heat treatment also effectively minimizes internal defects such as pores, internal cracks and delamination. The tensile strength and microhardness were further examined, according to the various microstructures. The as-built samples had a high tensile strength (UTS) of 1246 ± 10 MPa, but they displayed low ductility with limited elongation of 4.64 ± 0.9% and lower microhardness. The HT sample exhibited higher yield strength (YS). The HT sample exhibited a lowered tensile strength 1138 ± 5 MPa but showed an improved elongation behavior of up to 6.35 ± 0.2% and relatively more microhardness. The annealing HT caused a decrease in UTS, but it also enhanced ductility, microhardness and YS which make it suited for aerospace and automotive applications.