Mechanical properties of α + β type titanium alloys fabricated by metal injection molding with targetting biomedical applications

Metal injection molding (MIM) is a cost-saving process for fabricating products that have complicated shapes with a very high accuracy of size. It is expected that MIM will be employed as a new process for fabricating orthopedic and dental products with complicated shapes. The mechanical properties of Ti-6Al-4V, particularly its tensile and fatigue properties, fabricated by MIM (Ti64) were investigated to determine their suitability for medical applications. In order to improve the reliability of Ti64 for biomedical applications, the effects of heat treatments, and the addition of an element (Mo) on its mechanical properties were also investigated. The 0.2% proof stress, tensile strength and elongation of Ti64 are approximately 740 MPa, 850 MPa, and 12%, respectively. The volume fraction of the pores is around 1.1%. The tensile strength of Ti64 subjected to heat treatment at 1323 K for 3.6 ks followed by air cooling and hot rolling increases by around 24%. However, it is difficult to improve the strength-elongation balance because the elongation decreases after heat treatment and hot rolling. The strength-elongation balance of Ti64 is improved by hot isostatic pressing (HIP): the tensile strength and elongation are around 960 MPa and 13%, respectively. The tensile strength of Mo added Ti64 that contains Mo (Ti-6Al-4V-3Mo) increases by around 15% in comparison with that of Ti64. The elongation of both the alloys is almost the same. The size of the pores of Ti64 is reduced drastically by HIP. The fatigue strengths of Ti64 subjected to HIP is the highest in the low- and high-cycle fatigue-life regions. Its fatigue strength is comparable to that of wrought Ti-6A1-4V.