Abstract

This experimental program investigated the effects of cryogenic temperature treatment on the mechanical properties and microstructure of Nickel-Titanium shape memory alloys. Mechanical testing including tensile and hardness were carried out after having undergone various cryogenic temperature treatment conditions, and the results were compared.
Experimental results showed an increase in material hardness was observed when compared to untreated materials. With both steady-state and cyclical conditioning, an increase of approximately 2.0% and 8.7% was observed, respectively. Furthermore, with respect to the cyclical temperature treatment exposures, an increase in both estimated final yield and tensile strengths was also observed, resulting in relative increases of 9.5% and 3.2%, respectively, when again compared to as-received materials. It was concluded these increases in mechanical properties were primarily due to both an increase in the formation of austenite throughout the material’s microstructure, and the overall reduction in martensite grain size structure throughout the sample. The material’s inherent twinning process of the microstructure, coupled with thermally stress-induced martensite plate growths at the martensite transformation temperature are potential contributors to this transformation in the microstructure, resulting in the observed change in mechanical properties.