Properties and potential of two (Ni,Pt)Ti alloys for use as high-temperature actuator materials

Ronald Noebe; Darrell Gaydosh; Santo Padula II; Anita Garg; Tiffany Biles; Michael Nathal

doi:10.1117/12.598492

16 May 2005 Properties and potential of two (Ni,Pt)Ti alloys for use as high-temperature actuator materials

Ronald Noebe, Darrell Gaydosh, Santo Padula II, Anita Garg, Tiffany Biles, Michael Nathal

Proceedings Volume 5761, Smart Structures and Materials 2005: Active Materials: Behavior and Mechanics; (2005) https://doi.org/10.1117/12.598492
Event: SPIE Smart Structures and Materials + Nondestructive Evaluation and Health Monitoring, 2005, San Diego, California, United States

Abstract

The microstructure, transformation temperatures, basic tensile properties, shape memory behavior, and work output for two (Ni,Ti)Pt high-temperature shape memory alloys have been characterized. One was a Ni₃₀Pt₂₀Ti₅₀ alloy (referred to as 20Pt) with transformation temperatures above 230 °C and the other was a Ni₂₀Pt₃₀Ti₅₀ alloy (30Pt) with transformation temperatures above 530 °C. Both materials displayed shape memory behavior and were capable of 100% (no-load) strain recovery for strain levels up to their fracture limit (3-4%) when deformed at room temperature. For the 20Pt alloy, the tensile strength, modulus, and ductility dramatically increased when the material was tested just above the austenite finish (Af) temperature. For the 30Pt alloy, a similar change in yield behavior at temperatures above the Af was not observed. In this case the strength of the austenite phase was at best comparable and generally much weaker than the martensite phase. A ductility minimum was also observed just below the As temperature in this alloy. As a result of these differences in tensile behavior, the two alloys performed completely different when thermally cycled under constant load. The 20Pt alloy behaved similar to conventional binary NiTi alloys with work output due to the martensite-to-austenite transformation initially increasing with applied stress. The maximum work output measured in the 20Pt alloy was nearly 9 J/cm³ and was limited by the tensile ductility of the material. In contrast, the martensite-to-austenite transformation in the 30Pt alloy was not capable of performing work against any bias load. The reason for this behavior was traced back to its basic mechanical properties, where the yield strength of the austenite phase was similar to or lower than that of the martensite phase, depending on temperature. Hence, the recovery or transformation strain for the 30Pt alloy under load was essentially zero, resulting in zero work output.

Citation Download Citation

Ronald Noebe, Darrell Gaydosh, Santo Padula II, Anita Garg, Tiffany Biles, and Michael Nathal "Properties and potential of two (Ni,Pt)Ti alloys for use as high-temperature actuator materials", Proc. SPIE 5761, Smart Structures and Materials 2005: Active Materials: Behavior and Mechanics, (16 May 2005); https://doi.org/10.1117/12.598492

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