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Materials 2019, 12(5), 798; https://doi.org/10.3390/ma12050798

Effect of Stoichiometry on Shape Memory Properties and Functional Stability of Ti–Ni–Pd Alloys

1
Graduate School of Pure and Applied Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8573, Japan
2
Faculty of Pure and Applied Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8573, Japan
3
Foundation for Advancement of International Science, Tsukuba, Ibaraki 305-0821, Japan
*
Authors to whom correspondence should be addressed.
Received: 15 February 2019 / Revised: 4 March 2019 / Accepted: 6 March 2019 / Published: 8 March 2019
(This article belongs to the Section Smart Materials)
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Abstract

Ti–Ni–Pd shape memory alloys are promising candidates for high-temperature actuators operating at above 373 K. One of the key issues in developing high-temperature shape memory alloys is the degradation of shape memory properties and dimensional stabilities because plastic deformation becomes more pronounced at higher working temperature ranges. In this study, the effect of the Ti:(Ni + Pd) atomic ratio in TixNi70−xPd30 alloys with Ti content in the range from 49 at.% to 52 at.% on the martensitic transformation temperatures, microstructures and shape memory properties during thermal cycling under constant stresses were investigated. The martensitic transformation temperatures decreased with increasing or decreasing Ti content from the stoichiometric composition. In both Ti-rich and Ti-lean alloys, the transformation temperatures decreased during thermal cycling and the degree of decrease in the transformation temperatures became more pronounced as the composition of the alloy departed from the stoichiometric composition. Ti2Pd and P phases were formed during thermal cycling in Ti-rich and Ti-lean alloys, respectively. Both Ti-rich and Ti-lean alloys exhibited superior dimensional stabilities and excellent shape memory properties with higher recovery ratio and larger work output during thermal cycling under constant stresses when compared with the alloys with near-stoichiometric composition. View Full-Text
Keywords: shape memory effect; martensitic transformation; high-temperature shape memory alloy; thermal cycling; precipitation; stoichiometry; differential scanning calorimetry shape memory effect; martensitic transformation; high-temperature shape memory alloy; thermal cycling; precipitation; stoichiometry; differential scanning calorimetry
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
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Hattori, Y.; Taguchi, T.; Kim, H.Y.; Miyazaki, S. Effect of Stoichiometry on Shape Memory Properties and Functional Stability of Ti–Ni–Pd Alloys. Materials 2019, 12, 798.

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