Dense layer, microstructure and mechanical properties of Ti-6Al-4V alloy prepared by metal injection molding

Abstract Metal injection molding (MIM) is one of the latest technologies for fabricating titanium-based products. However, there have been few systematic studies on the definition and generation mechanism of surface porosity of injection molded Ti-6Al-4V and its relationship with powder, process and mechanical properties so far. In this paper, MIM was selected to prepare Ti-6Al-4V alloy, and the effects of sintering and subsequent hot isostatic pressing (HIP) process on the microstructure and mechanical properties were investigated. The results indicate that Ti-6Al-4V alloy formed a dense layer after sintering because of the temperature gradient from surface to core. The thickness of dense layer, grain size, grain morphology, and grain orientation are the key factors that determining the mechanical properties of Ti-6Al-4V alloy. Under the condition of sintering at 1000℃ with HIP process, Ti-6Al-4V alloy formed a thick dense layer of 290 µm, equiaxed grains with the small average grain size of 16 µm, and a high proportion of high-angle grain boundaries of 88.9%. Due to the optimized microstructure, Ti-6Al-4V alloy exhibited excellent mechanical properties, with the tensile strength of 1067 MPa, yield strength of 997 MPa, and elongation of 17.5%. This approach can serve as a guideline for other MIM materials.