Fatigue Property of Super-Elastic Ti–Ni Alloy Dental Castings

Abstract

Ti–Ni alloy is a promising material in the medical and dental fields due to its special mechanical properties, especially super-elasticity. Since dental prostheses are generally used under repetitive stress condition, fatigue properties of Ti–Ni alloy castings were investigated in this study. Ti–50.85Ni (mol%) alloy ingots were used for casting, which exhibited super-elasticity at 310 K in tensile test. Specimens were prepared with a centrifugal casting machine and a magnesia-based mold material. Fatigue test was performed at 310 K under repetitive loading condition with sine-waved load. The minimum stress was set at 0 MPa to evaluate the fatigue properties and change in residual strain. The maximum stress was set in the appropriate range considering the tensile property. Ultimate tensile strength and elongation to fracture of Ti–Ni alloy castings were 732 MPa and 10.6%, respectively, which were between those of CP-Ti and Ti–6Al–4V alloy castings. The fatigue limit of Ti–Ni alloy casting (206 MPa) was equivalent to or higher than that of CP-Ti or Ti–6Al–4V alloy. There was linear correlation between the fatigue ratios to ultimate tensile strength and the elongation to fracture for Ti–Ni alloy, CP-Ti and Ti–6Al–4V alloy castings, while Ti–Ni alloy showed high fatigue ratio to proof stress, which appears to relate to the twin deformation by stress-induced martensitic transformation. The stress-strain properties of Ti– Ni alloy castings were evaluated to be stable, and it is possible to utilize the super-elasticity in cast dental prostheses.