1999 Volume 42 Issue 2 Pages 243-248
Shape memory alloys(SMAs) are designed to be used as structural elements at elevated temperatures. The material used in this study was Ni-Ti-Nb SMA with a chemical composition of 51 wt% Ni, 38 wt% Ti, and 11 wt% Nb. The shape-recovery finishing temperature was around 350 K. When the material was heated from room temperature(293 K)to high temperature(561 K), the tensile strength and 0.2%-proof stress slightly decreased, while the elongation and reduction of area increased. Young's modulus increased with the temperature, up to 673 K. The fatigue strength at 561 K in air and in water was slightly higher than at 293 K in air. The fatigue limit in water was close to that in air at 561 K. The fatigue limits at 561K were about 290, 240, and 150 MPa for stress ratios of -1, 0, and 0.5 respectively. Fatigue cracks were found to initiate in the Ti-rich precipitates in the sub-surface, indicating that the fatigue strength is affected by the mean stress. The Ni-Ti-Nb SMA was found to have sufficient mechanical and fatigue strengths to be used as a structural element at elevated temperatures in water.
JSME international journal. Ser. 1, Solid mechanics, strength of materials
JSME international journal. Ser. A, Mechanics and material engineering
JSME international journal. Ser. 3, Vibration, control engineering, engineering for industry
JSME international journal. Ser. C, Dynamics, control, robotics, design and manufacturing