Phase transformations in Pd- and Ni-rich Ti-Pd-Ni alloys

It has been found that Ti₄₅Pd₄₅Ni₁₀ alloy shows peculiar phase transformations. Upon heating in DSC measurement, an endothermic reaction occurs firstly around 373 K, which corresponds to the reverse martensitic transformation from B19 to B2 structure. Subsequently, a pair of exothermic and endothermic peaks is observed from 550 to 740 K, which is due to the appearance and disappearance of new order phase with long period stacking structure. One of characteristic feature in electron diffraction pattern of the new phase is superlattice spots at 1/8 position in the row of reflections of 111_B2*. Finally, an exothermic reaction which corresponds to the formation of Ti₂(PdNi)₃ phase is detected around 850 K. More interesting phenomenon, which is the parent phase stabilization with low temperature aging below 500 K, is discovered. The ω-like diffuse reflections with rather strong intensity are observed in electron diffraction patterns taken from the stabilized B2 phase. Morphological and crystallographic aspects of the new order phase are also discussed.