X-ray and microstructural investigation of NiTiPt alloys homogenised at intermediate to high temperatures

The structural evolution of a Ni-rich NiTiPt alloy (Ni50Ti42.5Pt7.5) is studied here as a function of homogenisation temperature. The biphasic microstructure of the as-cast Ni50Ti42.5Pt7.5 alloy consisted of a high-Pt lath type structure that was dispersed in a martensitic NiTiPt matrix. Homogenisation of the as-cast structure at intermediate temperatures (825-925 °C) resulted in the redistribution of the dendritic second phase into a faceted structure. The hardness of the alloy decreased with increasing temperatures within this intermediate homogenisation temperature range due to breaking of the as-cast structure. Homogenisation of the alloys at higher temperatures e.g. 1100 and 1200 °C, resulted in the reformation of a lathed structure with an associated precipitation hardening due to the due to the formation of fine Ni-rich precipitates.