Ni-Ti-Nb系形状記憶合金の機械的特性と破壊靱性に及ぼす負荷速度の影響

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The static tensile and fracture toughness properties of Ni-Ti-Nb shape memory alloy (SMA) were examined at room temperature and 561 K. Its chemical composition is 51 wt.% Ni, 38 wt.% Ti, and 11 wt.% Nb. The shape recovery temperature is around 350 K. The tensile strength and the reduction of area at 561 K are slightly higher than those at 293 K. And the 0.2% proof stress, tensile strength, and reduction of area are constant with increasing loading rate below 10000 MPa/s. With increasing temperature K_<max> slightly decrease below 413K, but slightly increases below 561 K, and K_Q slightly decreases below 561 K. With increasing loading rate below 10000 MPa√<m> K_<max> is constant, but K_Q increases. The fracture toughness of this SMA is lower than that of general structural elements, because, micro-cracks initiate from the Ti-rich precipitates at the bottom of a dimple. K (J_<IC>) was obtained as 51.7 MPa√<m>, so the material crack was evaluated conservatively using at K (J_<IC>). In conclusion Ni-Ti-Nb SMA has sufficient mechanical and fracture toughness strength for structural elements at elevated temperatures.
社団法人日本機械学会の論文
1999-12-25