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Phase transformation and creep behavior in Ti50Pd30Ni20 high temperature shape memory alloy in compression
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Paper Abstract

The creep behavior and the phase transformation of Ti50Pd30Ni20 High Temperature Shape Memory Alloy (HTSMA) is investigated by standard creep tests and thermomechanical tests. Ingots of the alloy are induction melted, extruded at high temperature, from which cylindrical specimens are cut and surface polished. A custom high temperature test setup is assembled to conduct the thermomechanical tests. Following preliminary monotonic tests, standard creep tests and thermally induced phase transformation tests are conducted on the specimen. The creep test results suggest that over the operating temperatures and stresses of this alloy, the microstructural mechanisms responsible for creep change. At lower stresses and temperatures, the primary creep mechanism is a mixture of dislocation glide and dislocation creep. As the stress and temperature increase, the mechanism shifts to predominantly dislocation creep. If the operational stress or temperature is raised even further, the mechanism shifts to diffusion creep. The thermally induced phase transformation tests show that actuator performance can be affected by rate independent irrecoverable strain (transformation induced plasticity + retained martensite) as well as creep. The rate of heating and cooling can adversely impact the actuators performance. While the rate independent irrecoverable strain is readily apparent early in the actuators life, viscoplastic strain continues to accumulate over the lifespan of the HTSMA. Thus, in order to get full actuation out of the HTSMA, the heating and cooling rates must be sufficiently high enough to avoid creep.

Paper Details

Date Published: 30 March 2010
PDF: 7 pages
Proc. SPIE 7644, Behavior and Mechanics of Multifunctional Materials and Composites 2010, 76440Q (30 March 2010); doi: 10.1117/12.851737
Show Author Affiliations
Parikshith K. Kumar, Texas A&M Univ. (United States)
Uri Desai, Texas A&M Univ. (United States)
James Monroe, Texas A&M Univ. (United States)
Dimitris C. Lagoudas, Texas A&M Univ. (United States)
Ibrahim Karaman, Texas A&M Univ. (United States)
Ron Noebe, NASA Glenn Research Ctr. (United States)
Glenn Bigelow, NASA Glenn Research Ctr. (United States)

Published in SPIE Proceedings Vol. 7644:
Behavior and Mechanics of Multifunctional Materials and Composites 2010
Zoubeida Ounaies; Jiangyu Li, Editor(s)

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