Examination of phase changes in the CuAl high-temperature shape memory alloy with the addition of a third element

In the present study, a ternary CuAl-based alloy was produced by adding 2% chromium, niobium, titanium and hafnium instead of 2% copper from the Cu₈₈Al₁₂ (% in mass) shape memory alloy, and the phase changes in the alloy were examined. As a result of the X-ray analyses performed at room temperature, the α phase, which is rich in copper, was detected in the main sample, i.e., the Cu₈₈Al₁₂ alloy, and the β₁¹ and γ₁^ı phases were detected in the four of the Cu₈₆Al₁₂Cr₂, Cu₈₆Al₁₂Nb₂, Cu₈₆Al₁₂Ti₂ and Cu₈₆Al₁₂Hf₂ alloys. All of phases were clearly seen in SEM images. As a result of the mapping performed during chemical analysis, it was observed clearly that there appeared a precipitation phase in the Cu₈₆Al₁₂Cr₂, Cu₈₆Al₁₂Nb₂, Cu₈₆Al₁₂Ti₂ alloys due to the additions. It was also observed that the additions were effective in forming a martensite phase in the Cu₈₈Al₁₂ alloy. In differential scanning calorimetry (DSC) measurements, which were taken to support these measurements, no martensitic phase transformations were detected in dual primary alloy (Cu₈₈Al₁₂); however, a clear martensite phase transformation was detected in ternary alloys (Cu₈₆Al₁₂Cr₂, Cu₈₆Al₁₂Nb₂, Cu₈₆Al₁₂Ti₂ and Cu₈₆Al₁₂Hf₂) in the first DSC measurement. Then, when the DSC cycle was applied to the ternary alloy, both the austenite transformation and martensite transformation temperatures were clearly seen, and it was claimed that all the alloys showed high-temperature shape memory alloy properties.