The compositional stability of the P-phase in Ni-Ti-Pd shape memory alloys

The precipitation of the P-phase in Ni-Ti-Pd and Ni-Ti-Pt shape memory alloys has been shown to dramatically increase the martensitic transformation temperature and strength in Ni-rich ternary alloys, yet little is known about the phase's compositional stability. Therefore, the compositional limits of the P-phase have been systematically studied by varying the Pd and Ni content while maintaining the general P-phase Ti-11(Ni + Pd)(13) stoichiometry. Each alloy was solutionized at 1050 degrees C followed by water quenching, and aging at 400 degrees C for 100 h. Four distinct phases were identified by electron and x-ray diffraction: Ti2Pd3, B2 NM, P- and P1-phases. The latter precipitate phases became more stable with increasing Ni at the expense of the Pd content. Atom probe tomography revealed the P-phase composition to be 45.8Ti-29.2Ni-25Pd (at.%) or Ti-11(Ni7Pd6) as compared to the P1-phase 44.7Ti-45.8Ni -9APd (at.%) or Ti5Ni5Pd. (C) 2015 Elsevier Ltd. All rights reserved.