Selective Laser Melted Ti-6Al-4V Alloy after Post-Heat Treatments: Microstructure, Mechanical Properties and Fatigue Behavior

In the present work, an investigation is conducted into the effects of heat treatment (700, 800, 900 and 1000 °C) on the microstructure, mechanical properties and fatigue behavior of Ti-6Al-4V alloy fabricated by selective laser melting (SLM). According to the results of microstructure analysis, compared with the Ti-6Al-4V alloy under the initial SLM condition, the sample shows a completely different microstructure after heat treatment. With the increase in heat treatment temperature, the dominant acicular α' martensite in Ti-6Al-4V alloy is decomposed into fine (α + β) lamellae, and the microstructure is significantly coarsened. When the heat treatment temperature exceeds 800 °C, the heat treatment sample develops a finer (α + β) dual-phase matrix microstructure. As revealed by the test of mechanical properties, the samples heat treatment at 900 °C exhibits higher yield strength, higher tensile strength, finer microstructure and greater elongation at break. To be specific, the tensile strength, yield strength and elongation are 921 Mpa, 819 MPa and 16.1%, respectively. According to the results of high cycle fatigue test, the fatigue performance of SLM Ti-6Al-4V alloy is significantly improved by conducting stress relief heat treatment at 900 °C for 10⁷ cycles, with the fatigue strength reaching 190 MPa.