Influence of Heat Treatment on the Microstructure and Mechanical Properties of TC4 Alloy Fabricated by Selective Laser Melting

Abstract

The TC4 (Ti6Al4V) titanium alloy fabricated by Selective Laser Melting (SLM) has gained significant attention in recent years due to its exceptional properties, including high strength-toweight ratio, excellent corrosion resistance, and biocompatibility. This study examines the effect of heat treatment on the microstructure, phase composition, and mechanical properties of SLMfabricated TC4 alloy, to provide a more comprehensive understanding of the material's behavior under varying thermal conditions. Experimental results demonstrated that the as-deposited TC4 alloy has a relative density above 0.99. The as-deposited TC4 alloy was mainly composed of closepacked hexagonal structure α/ α′ phases. In addition, a small amount of β-phase was also detected. After annealing treatment, the TC4 alloy showed a similar phase composition. The microstructure of the as-deposited TC4 alloy was composed of acicular martensite a′phase accompanied by α-phase in β-matrix. After annealing treatment, the acicular α′ martensite decomposed, transforming the microstructure into a lamellar structure consisting of α- and β-phases. The microhardness was to 351.7 HV_0.2, the tensile strength was approximately 1,120 MPa, and the yield strength comprised approximately 1,080 MPa of the TC4 alloy fabricated by SLM. The tensile fracture surface of the asdeposited alloy demonstrated a mixture of brittle and ductile fracture. A quasi-cleavage river pattern and a small amount of irregular dimples can be observed. After annealing treatment, the elongation increased to 16.5% due to a slight decrease in hardness and tensile strength. The Vickers hardness was 323.1 HV_0.2, the tensile strength was approximately 960 MPa, and the yield strength was about 925 MPa, respectively. The amounts and the size of dimples increased significantly and displayed typical ductile fracture. This research would provide valuable insights into optimizing the performance of SLM-fabricated TC4 alloys for various engineering applications.