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

Parikshith K. Kumar; Uri Desai; James Monroe; Dimitris C. Lagoudas; Ibrahim Karaman; Ron Noebe; Glenn Bigelow

doi:10.1117/12.851737

30 March 2010 Phase transformation and creep behavior in Ti₅₀Pd₃₀Ni₂₀ high temperature shape memory alloy in compression

Parikshith K. Kumar, Uri Desai, James Monroe, Dimitris C. Lagoudas, Ibrahim Karaman, Ron Noebe, Glenn Bigelow

Author Affiliations +

Proceedings Volume 7644, Behavior and Mechanics of Multifunctional Materials and Composites 2010; 76440Q (2010) https://doi.org/10.1117/12.851737
Event: SPIE Smart Structures and Materials + Nondestructive Evaluation and Health Monitoring, 2010, San Diego, California, United States

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.

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Parikshith K. Kumar, Uri Desai, James Monroe, Dimitris C. Lagoudas, Ibrahim Karaman, Ron Noebe, and Glenn Bigelow "Phase transformation and creep behavior in Ti₅₀Pd₃₀Ni₂₀ high temperature shape memory alloy in compression", Proc. SPIE 7644, Behavior and Mechanics of Multifunctional Materials and Composites 2010, 76440Q (30 March 2010); https://doi.org/10.1117/12.851737

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