Thermal and Electrical Properties of Phase Change Materials Obtained by Spark Plasma Sintering

This work investigates NiTi and NiTiCu shape memory alloys as phase change materials. The thermal and electrical properties of SMAs depend on composition, phases, microstructure, density and, last but not least, the processing route. The samples used in this study were made from Ni, Ti and/or Cu elemental powder with different compositions and were obtained using spark plasma sintering. The use of neutron diffraction allowed the identification of the main phases of NiTi and NiTiCu microstructures. The majority phase identified by neutron diffraction was B19’, corresponding to monoclinic structure, but also B2 with cubic structure, respectively. These measurements allowed a direct correlation of the microstructure evolution with thermal and electric properties. The thermal properties of conductivity, diffusivity and specific heat were determined by the laser flash method from 25°C up to 300°C. Measurements at room temperature of resistivity or electrical resistance were conducted too.