Variation of material properties in tilt-cast Cu-Al-Ni alloy

CuAl-based alloys have long been a promising option for high temperature SMAs (HTSMA) due to cost advantages over NiTi-based high-temperature SMAs. CuAlNi alloys in particular exhibit excellent shape memory effects as well as phase stability at temperatures up to 250°C. Due to the strong influence of the chemical composition on transformation temperatures, fabrication processes need to avoid inhomogeneities in the material. While multiple remelting processes achieve that goal, single step inductive melting is preferable in terms of productivity, especially for small alloy batches. In preparation for future work on high-temperature CuAlNi alloys, the goal in this and consecutive work is to characterize, and reduce, the variation of material properties and microstructure material prepared by vacuum-induction melting of pure elements and tilt-casting. Considerable consistency of transformation temperatures and phase composition in each individual casting, as well as between castings with identical parameters, could be achieved. In this paper we will present the first results in alloys with target chemical compositions ranging from Cu12.5wt.%Al4wt.%Ni to Cu13.2wt.%Al4wt.%Ni, homogenized at 850°C for 30 mins and quenched in iced water. These alloys should exhibit transformation temperatures between 196,8 °C to 260 °C (A_p) and 175,9 °C to 228,6 °C (M_p). In first casting attempts, material casted at identical parameters showed a deviation of less than 3 K for A_p, but a deviation of up to 6 K for M_p, presumably connected to process variations during heat treatment. A further obstacle to overcome is the inconsistency between the Ni weight fraction and the expected value.