Microstructures and mechanical behaviors of Ti-30Nb-1Fe-xHf alloys

Abstract

Effects of iron (1mass%) and hafnium (1-7 mass%) on the microstructure and mechanical properties of Ti-30Nb base alloys were investigated in this study. Experimental results indicate that the addition of 1 mass% Fe to the Ti-30Nb alloy transforms the original α + β+ ω structure into a single β phase structure. Accompanying the structure change, both the tensile strength and 0.2% proof stress were reduced by some 15%, while the elastic modulus was reduced from 80 GPa to 68 GPa. Regarding the effect of Hf, precipitation of sporadic ω phase in the otherwise complete β phase structure can be detected when hafnium is added. An addition of just 1 mass% Hf to the Ti-30Nb-1Fe alloy increases the tensile strength and 0.2% proof stress by 32% and 27%, respectively, while slightly decreasing the elastic modulus by some 10%. The Ti-30Nb-1Fe-1Hf alloy has relatively high strength (∼914MPa T. S.), reasonable ductility (∼10% El), and an elastic modulus of around 62GPa. Consequently, the ratio of 0.2% proof stress to elastic modulus increases moderately. The ratio of 0.2% proof stress to elastic modulus of Ti-30Nb-1Fe-1Hf was found to be 1.39 × 10-2, which was around 1.8 times higher than Ti-6Al-4V (0.78 × 10-2), and around 3.5 times higher than c.p.Ti (0.4 × 10-2). Hafnium content exceeding 1 mass% gives no further improvement in the ratio of 0.2% proof stress to elastic modulus. From the results obtained here, Ti-30Nb-1Fe-1Hf alloy has excellent potential for orthopedic implant applications.