Thermal Characterization of Nickel Titanium Shape Memory Alloys via Frequency Domain Thermoreflectance

Shape Memory Alloys (SMAs) have a wide range of applications due to their unique thermal-mechanical properties caused by the austenitic-martensitic phase transformation. One of the most promising applications is in elastocaloric cooling, which has the potential to become a small, environmentally friendly, and efficient alternative to vapor-compression systems. The SMA with the most promise is Nickel Titanium (NiTi) due to its stability and thermal-mechanical performance. The mechanisms that govern the thermal properties of NiTi are not well characterized and may be affected grain size, strain, and temperature. Using the frequency-domain thermoreflectance (FDTR) method, the thermal properties of NiTi SMAs with different grain sizes will be determined as a function of strain and temperature. FDTR is a pump-probe non-contact optical technique that can accurately determine the thermal properties such as heat capacity, thermal conductivity, and thermal boundary conductance of thin films and bulk materials. It is expected that measuring the thermal properties of NiTi will help to determine its viability as a candidate material for strain-induced elastocaloric cooling.