Characterization of Ternary NiTiPd High-Temperature Shape-Memory Alloys under Load-Biased Thermal Cycling

• Published in: Metallurgical and materials transactions. A, Physical metallurgy and materials science Vol. 41; no. 12; pp. 3065 - 3079
• Main Authors: Bigelow, Glen S., Padula, Santo A., Garg, Anita, Gaydosh, Darrell, Noebe, Ronald D.
• Format: Journal Article
• Language: English
• Published: Boston Springer US 01-12-2010; Springer; Springer Nature B.V
• Subjects: Alloys; Applied sciences; Characterization and Evaluation of Materials; Chemistry and Materials Science; Exact sciences and technology; Materials Science; Metallic Materials; Metallurgy; Metals. Metallurgy; Nanotechnology; Residual stress; Structural Materials; Surfaces and Interfaces; Thin Films; Transformation Temperature; Transformation Strain; Martensite; Computer Numerically Control; NiTi Alloy; Thermal cycle; Temperature; High temperature; Shape memory alloy
• ISSN: 1073-5623; 1543-1940
• DOI: 10.1007/s11661-010-0365-5

While NiTiPd alloys have been extensively studied for proposed use in high-temperature shape-memory applications, little is known about the shape-memory response of these materials under stress. Consequently, the isobaric thermal cyclic responses of five (Ni,Pd)
49.5
Ti
50.5
alloys with constant stoichiometry and Pd contents ranging from 15 to 46 at. pct were investigated. From these tests, transformation temperatures, transformation strain (which is proportional to work output), and unrecovered strain per cycle (a measure of dimensional instability) were determined as a function of stress for each alloy. It was found that increasing the Pd content over this range resulted in a linear increase in transformation temperature, as expected. At a given stress level, work output decreased while the amount of unrecovered strain produced during each load-biased thermal cycle increased with increasing Pd content, during the initial thermal cycles. However, continued thermal cycling at constant stress resulted in a saturation of the work output and nearly eliminated further unrecovered strain under certain conditions, resulting in stable behavior amenable to many actuator applications.