The production of CuAl based high temperature shape memory alloys and investigation of their oxidation behavior

The Production of CuAl based high temperature shape memory alloys and investigation of their oxidation behavior In the present study, a ternary CuAl-based alloy was produced by adding 2% Chrome, 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 γ1ı 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 made to support these measurements, no martensitic phase transformations were detected in dual primary alloy; however, a clear martensite phase transformation was detected in ternary alloys 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. Besides, the oxidation properties of CuAl and Cu86Al12-X2 (X = Cr, Nb, Ti, Hf) shape memory polycrystalline alloys, which are inexpensive and industrially usable, were studied from the shape memory alloy group. It is known that these alloys are heat treated at high temperatures up to 900 oC for the development of these alloys. For this reason, it is important to examine the oxidation properties of alloys with temperature at this frequently used temperature value. Alloys were oxidized with TG / DTA (thermogravimetric analysis) device and oxidation constant values were calculated. The alloy Cu86Al12Hf2 with the highest oxidation constant was found to be the lowest alloy Cu86Al12Nb2 alloy. In the surface morphology studies made with SEM-EDX, except for Cu88Al12 and Cu86Al12Ti2 alloys, coat-like oxide layers were observed in other alloys, whereas Cu88Al12 and Cu86Al12Ti2 alloys were found to have oxide cluster regions. In all alloys, the x-ray analysis results of the oxide layers are also found. Keyword: CuAl based, element addition, Cu rich phase, DSC cycle, high temperature shape memory (HTSM), oxidation, oxide phase