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Properties and Potential of Two (ni,pt)ti Alloys for Use as High-temperature Actuator MaterialsThe 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 about 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 about the austenite finish (A(sub f)) temperature. For the 30Pt alloy, a similar change in yield behavior at temperatures above the A(sub f) was not observed. In this case the strength of the austentite phase was at best comparable and generally much weaker than the martensite phase. A ductility minimum was also observed just below the A(sub s) 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/cu cm 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.
Document ID
20050185200
Document Type
Preprint (Draft being sent to journal)
Authors
Noebe, Ronald (NASA Glenn Research Center Cleveland, OH, United States)
Gaydosh, Darrell (Ohio Aerospace Inst. Brook Park, OH, United States)
Padula, Santo, II. (NASA Glenn Research Center Cleveland, OH, United States)
Garg, Anita (Toledo Univ. OH, United States)
Biles, Tiffany (Ohio Aerospace Inst. Brook Park, OH, United States)
Nathal, Michael (NASA Glenn Research Center Cleveland, OH, United States)
Date Acquired
September 7, 2013
Publication Date
February 10, 2005
Subject Category
Metals and Metallic Materials
Meeting Information
Smart Structures and Materials 2005: Behavior and Mechanics(San Diego, CA)
Funding Number(s)
WBS: WBS 22-714-70-63
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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