Large thermal hysteresis and high cycling stability induced by aging in a NiTiNb alloy

This study compares the transformation behavior and thermal cycling stability of a Ni₅₁Ti_48.5Nb_0.5 (at.%) alloy in its solution-treated and low-temperature-aged state. Being Ni-rich of the B2 stoichiometry, low-temperature aging caused the formation of clusters and led to B2 disordering and lattice distortions. In consequence, the alloy exhibited an enlarged B2-B19ʹ transformation thermal hysteresis of approximately 62 °C, in comparison to 40 °C of the solution-treated counterpart. The aged alloy also showed a high cycling stability during 100 thermal transformation cycles, with <1 °C variation of the martensitic transformation temperature as compared to the 20 °C decrement for the solution-treated sample under the same condition. The large thermal hysteresis and high cycling stability of the aged samples may be attributed to the short-range compositional heterogeneity and local lattice distortion which inhibit the interfacial motion and the mobility of dislocations during transformation cycles.