Effects of heat treatment temperature and thermal cycling on phase transformations in Ni–Ti–Cr alloy

Abstract

The transformation behavior of 45% cold worked Ni–Ti–Cr alloy, in a wide temperature range from +90° to −170°C has been studied as a function of heat treatment temperature by employing electrical resistivity probes. In this alloy, the R-phase is found to persist over a wide heat treatment temperature range. In the as-received sample and for heat treatments up to 400°C only the A↔R transformation has been found to prevail. For the intermediate heat treatment temperatures of 400–600°C, the complete A→R→M phase transformations takes place. At higher regions of heat treatment temperature, the R-phase has been found to decay, giving way to only the M↔A transformation. All the transformation temperatures are confined to below room temperature, for the samples heat treated up to 800°C. The effect of thermal cycling has also been studied in detail for heat treatment at selected temperatures. The thermal cycling is found to have no effect on the phase transformation whenever the R-phase is present and thermal cycling is found to promote the R-phase if the sample does not possess the R-phase initially.