Evaluation of influence factors on the microstructure, static and dynamic mechanical properties of injection molded Ti-6Al-4V based compacts by multiple addition of Mo and B Elements

Although the injection molded Ti alloys show sufficient tensile strength, their fatigue strength was significantly lower than that of wrought material. In this study, the effect of both additions of molybdenum and boron in the Ti-6Al-4V compacts on the microstructural refinement and strength was evaluated. The 4Mo-0.4B added compacts showed fine microstructure and resulted in high tensile strength. However, their fatigue strength was not improved. The degree of influence of oxygen content, relative density and grain size on the tensile strength was estimated, and the main factor of improving tensile strength was the grain refinement. Also, the cause that fatigue strength was not improved was the ratio of the maximum pore diameter to the grain diameter increased due to the microstructural refinement, so that the crack initiated from large pore.