New precipitate phase in Pd and Ni rich Ti-Pd-Ni shape memory alloys

The decomposition behavior and morphology of new precipitate in Pd and Ni rich Ti-Pd-Ni high temperature shape memory alloys have been studied by differential scanning calorimeter (DSC) and transmission electron microscopy (TEM). The precipitate is formed in Ti₄₈Pd_52-XNi_X alloys with X = 11 to 36 at%Ni. The precipitate appears with exothermic peak about 650 to 700 K and resolves with endothermic peak with about 740 to 780 K in DSC heating curve for the quenched alloys. The both peak temperatures increase with increasing Ni concentration. The shape of precipitate changes from cuboid to oval sphere shapes with increasing Ni concentration. The electron diffraction patterns of the precipitate are characterized by 1/4{111} superlattice reflections in B2 reciprocal space. The Ti₄₈Pd₃₁Ni₂₁ alloy aged under constrained condition at 673 K for 36 ks shows reversible shape memory effect during thermal cycling between room temperature and 523 K.