Study of the Thermal Properties of a Ni3Ta Shape Memory Alloy

Dilatation characteristics, thermal diffusivity, and thermal conductivity of a Ni3Ta shape memory alloy were studied over the temperature range from room temperature up to 950 A degrees C. The Ni3Ta alloy was investigated in both polycrystalline and single crystal forms. The shape memory effect was positive for the polycrystalline samples and negative for the single crystal. While the transformation temperature of the M (martensite) -> A (austenite) phase transformation was the same for both types of alloys and all measurements, the transformation temperature for the reverse phase transformation A -> M was dependent on the maximum cycle temperature. Higher maximum temperatures of the thermal cycle yielded lower transformation temperatures for the A -> M transformation. The thermal diffusivity and thermal conductivity of the austenite were higher than those of the martensite. No latent heat was found for the phase transformations.