Abstract
Ni24.7Ti50.3Pd25 and Ni24.7Ti49.3Pd25Sc1 high-temperature shape memory alloys were thermo-mechanically processed and characterized in the present study. The microstructural characteristics of cold-worked alloys showed the presence of shear/deformation bands and defects. TEM observation of cold-worked and annealed (400 to 500 °C) microstructures revealed the emergence of small fraction of newly formed martensite twins at 400 °C. With the increase in the annealing temperature from 400 to 500 °C, the fraction of the martensite twins in the microstructure was found to increase. The Ni24.7Ti50.3Pd25 and Ni24.7Ti49.3Pd25Sc1 alloys showed martensite finish temperature of ~180 °C and ~136 °C with an hysteresis of ~10 °C and ~9 °C, respectively. Ni24.7Ti50.3Pd25 and Ni24.7Ti49.3Pd25Sc1 alloys showed a recovery strain of 1.5% and 1.7% at a stress of 175 MPa. During cycling under load, the residual strain for the Ni24.7Ti49.3Pd25Sc1 alloy was found to be negligible as compared to ~0.2% in the Ni24.7Ti50.3Pd25 alloy. The results of the study indicate that these alloys have potential for use as high-temperature thermal actuator materials.
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