Mechanism of Heat Treatment Microstructural Evolution of TC4 Alloy Fabricated by Selective Laser Melting

The microstructural evolution of TC4(Ti6Al4V) alloy fabricated by selective laser melting(SLM) was studied by observing the microstructure of metallography and energy spectrum analysis.The results show that the martensite in the SLM-fabricated TC4 alloy is resolved completely after 800 ℃/2 h/FC heat treatment.After heat treatment at 950 ℃/2 h/WQ for 2 h, the needle martenite α'is generated on the metastable β matrix, alloy elements (e.g., Al, V) have obvious diffusion, and more V element migrate into the β matrix, the oversaturated β solid solids are formed.In the process of aging heat treatment, martensite α' is decomposed to lamellar α.The shaped nucleus of the crystal boundary emergence phase grows up to form a continuous crystal boundary α phase (α_GB).The secondary α phase (α_S)emerges from the metastable supersaturated β matrix, and the granular β phase spreads around α_S phase, forming β transition microstructure.The overall microstructure of the sample consists of intermittent α_GB, spherality α, basketweave α and β transition microstructure.