Effect of α + β region sintering on the mechanical properties of injection molded Ti-6Al-4V compacts

摘要

Injection molded Ti-6Al-4V compacts have normally a coarse lamellar microstructure, because it is sintered above the β transus temperature and it is cooled slowly in furnace. However, static mechanical properties such as tensile strength and ductility are equivalent to those of wrought materials, but they have the disadvantage that the fatigue strength is significantly lower than wrought materials. Therefore, improvement of fatigue strength is needed for injection molded Ti alloy compacts. In this study, injection molded Ti-6Al-4V compacts having equiaxed microstructure were prepared by sintering at α + β region temperature which is very lower than normal sintering temperature. When sintering is carried out in α + β region, sinterability is remarkably poor. Therefore, long-time sintering is required. Since the grain growth of the prior β grains was suppressed by the pinning effect of α grains and pores, it was possible to obtain the significantly fine grains as compared with the β region sintered compacts. The α + β region sintered compacts showed high strength, high elongation and also high fatigue strength. Furthermore, by applying HIP treatment, the mechanical properties were improved to satisfy the standard value of wrought Ti-6Al-4V material.