Abstract
Phase stability and mechanical properties of Ti-Zr based alloys containing Nb as β stabilizer were investigated. Phase stability of annealed and quenched alloys with various Nb concentration were examined by optical microscopy and X-ray diffractometry while mechanical properties of the alloys were evaluated by hardness and tensile tests. Young’s moduli were also measured by free-free beam resonance method.
Because Widmanstatten structure is observed in annealed 0-4 mol%Nb alloys while a two-phase structure is seen in annealed alloys containing more than 8 mol%Nb, it is considered that of α transus lays around 4-8 mol%Nb at room temperature. In the case of quenched alloys, alloys containing 0-4 mol%Nb exhibit martensitic transformed structure while alloys with more than 8 mol%Nb remain in a β single phase structure. Through microscopy and X-ray diffractometry, β phase stability in Ti-Zr-Nb system was considered and a Ti-Zr equiatomic isoplethal toward Nb corner in the Ti-Zr-Nb ternary phase diagram showing MS temperature was established.
Hardness and strength of β phase alloys are lower than those of martensitic alloys. Ductility of the former is larger than the latter. This might be caused by the deformability of bcc structure. Young’s moduli of β alloys are 74-90 GPa which are smaller than those of CP titanium (105 GPa). Those moduli correspond well with data in references.
From the results above, it is concluded that development of biomedical alloys with low elastic modulus is promising using titanium and zirconium as base materials and niobium as β stabilizer.
