The compositional stability of the P-phase in Ni–Ti–Pd shape memory alloys. (December 2015)

• Record Type: Journal Article
• Authors: Coppa, Anne C.; Kapoor, Monica; Noebe, Ron; Thompson, Gregory B.
• Is Part Of: Intermetallics. Volume 67(2015:Dec.)
• Page Start: 56
• Page End: 62
• Publication Date: 2015-12
• Subjects: Ni–Ti–Pd alloy -- Compositional stability -- P-phase -- P1-phase -- Atom probe tomography; Intermetallic compounds -- Metallography -- Periodicals; Metallic glasses -- Periodicals; Composés intermétalliques -- Métallographie -- Périodiques; 669.94
• DOI: 10.1016/j.intermet.2015.07.014
• Languages: English
• ISSNs: 0966-9795

Abstract

Abstract: 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 Ti11 (Ni + Pd)13 stoichiometry. Each alloy was solutionized at 1050 °C followed by water quenching, and aging at 400 °C for 100 h. Four distinct phases were identified by electron and x-ray diffraction: Ti2 Pd3, B2 NiTi, 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 Ti11 (Ni7 Pd6 ) as compared to the P1-phase 44.7Ti– 45.8Ni–9.4Pd (at.%) or Ti5 Ni5 Pd. Highlights: The compositional limits of the P-phase were systematically studied in Ni–Ti–Pd. Ti2 Pd3, B2 NiTi, P- and P1-phases were identified by electron and x-ray diffraction. P1-phase becomes more stable with increasing Ni at the expense of Pd content. APT revealed the P1-phase composition to be 44.7Ti– 45.8Ni–9.4Pd (at.%) or Ti5 Ni5 Pd.