Experimental determination of thermal and electrical properties of Ni-Ti shape memory wires

The thermal and electrical properties of shape memory alloys (SMA) are known to be different in their austenitic and martensitic phases. This paper addresses the determination of the phase-dependent heat capacity, thermal conductivity and electrical resistivity of a SMA wire. While the heat capacity measurements are relatively straightforward using a differential scanning calorimeter, the determination of the thermal conductivity and the electrical resistivity are more difficult in view of the possible non-uniformity in the material state of a SMA wire during a phase transformation. Experimental procedures are developed and used to determine these properties in either phase and, along with a previously developed finite-element code accounting for the non-uniform material states, the austenite and martensite properties are determined from the experimental data. For the SMA wire tested, the thermal conductivities of the austenite and martensite phases are determined to be 2.8×10-2 J (mm S K)-1 and 1.4×10-2 J (mm S K)-1 respectively, a difference of 100%. The electrical resistivities of the austenite and martensite phases are determined to be 8.371×10-4 Ω mm and 9.603×10-4 Ω mm respectively, a difference of about 14.7%.