Microstructural Evolution and Mechanical Performance of Ti-6Al-4V Fabricated by Laser Powder Bed Fusion

Ti-6Al-4V is a widely used titanium alloy known for its excellent corrosion resistance and high specific strength, making it ideal for critical applications in aerospace, biomedical, and power sectors. However, due to its poor machinability caused by complex deformation behaviour and thermal softening at elevated temperatures, additive manufacturing is preferred to fabricate near-net-shape components with minimal machining. This study investigates the microstructural evolution and mechanical behavior of Ti-6Al-4V alloy processed via Powder Bed Fusion using Laser Beam Melting (PBF-LB/M), under both as-built and post-processed conditions. The as-built samples demonstrated a high relative density of 99.3% with acicular α′ martensitic laths within prior α grains, resulting in a hardness of 365 VHN. Stress relieving at 590 °C for 2 h led to partial decomposition of martensite and formation of approximately 0.7% β-phase. Subsequent heat treatment at 900 °C transformed the microstructure into a refined α + β lamellar structure with 9.5% β-phase, reducing hardness to 329 VHN. Mechanical testing of heat-treated samples showed isotropic behaviour in both horizontal and vertical directions, with an ultimate tensile strength (UTS) of approximately 930 MPa, a yield strength (YS) of nearly 865 MPa, and a ductility of approximately 13%. These results underscore the importance of tailored post-processing to optimise the microstructure and mechanical performance of PBF-LB/M Ti-6Al-4V components for demanding engineering applications that require a balance of strength, ductility, and reliability.