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    THE EFFECT OF CHROMIUM ADDITION ON PHYSICAL PROPERTIES OF Cu-Al BASED HIGH TEMPERATURE SHAPE MEMORY ALLOY
    (Polska Akad Nauk, Polish Acad Sciences, Inst Metall & Mater Sci Pas, 2018) Cirak, Z. Deniz; Kok, M.; Aydogdu, Y.
    Cu-Al-based high temperature shape memory alloys are preferred commonly due to their cheap costs and shape memory properties. In recent years, studies have been conducted on developing and producing a new type of Cu-Al based shape memory alloy. In this study, the CuAl-Cr alloy system, which has never been produced before, is investigated. After production, the SEMEDX measurements were made in order to determine the phases in the Cu84-xAl12Crx+4 (x = 0, 4, 6) (weight %) alloy system; and precipitate phases together with martensite phases were detected in the alloys. The confirmations of these phases were made via x-ray measurements. The same phases were observed by XRD diffractogram of the alloys as well. The values of transformation temperature of alloys were determined with Differential Scanning Calorimetry (DSC) at 20 degrees C/min heating rate. According to the DSC results, the transformation temperature of the alloys varies between 320 degrees C and 350 degrees C. This reveals that the alloys show high temperature shape memory characteristics.
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    Effects of heat treatment temperatures on phase transformation, thermodynamical parameters, crystal microstructure, and electrical resistivity of NiTiV shape memory alloy
    (Springer, 2020) Kok, Mediha; Al-Jaf, Ahmed Omar Ali; Cirak, Z. Deniz; Qader, Ibrahim Nazem; Ozen, Ecem
    Changing physical property of NiTi shape memory alloy by adding new element and heat treatment technique has become interesting in the last decades. In this study, equiatomic NiTi alloy was doped by 1 and 5 atomic percentages of vanadium element. For each case, heat treatment was accomplished for 873, 973, 1073, and 1173 K, and its effect on phase transformation temperatures was analyzed by differential scanning calorimetry. Crystal structure and chemical compound found in XRD pattern showed the different situation for each case, e.g., TiO2 appeared in heat-treated samples, whereby the intensity of peaks varied by changing the temperature of heat treatment. In NiTi-5V alloy, each enthalpy, entropy, Gibbs free energy, and elastic energy were decreased by increasing heat treatment temperature, while grain size of the alloy extended with respect to non-heat-treated sample. Electrical resistivity of the alloys was measured as a function of temperature, which was increased by increasing vanadium composition and heat treatment temperature.
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    Investigation of the thermal and microstructural changes of CuAlNiNb quaternary shape memory alloys by different niobium amount
    (Springer Heidelberg, 2018) Cirak, Z. Deniz; Kok, Mediha
    Among the CuAl-based alloys, the most useful one is the CuAlNi ternary shape memory alloy. There are studies on the development of these alloys. In this study, beta-Nb element was added to the CuAlNi alloy as a fourth element at various rates. The effect of the doped Nb element on the martensitic transformation temperature of the CuAlNi-shape memory alloy was determined by differential scanning calorimetry (DSC). When the value of transformation temperature in quaternary CuAlNi alloys increased, as a result, austenite start and martensite start temperatures are close to each other. Crystalline structure analysis with X-ray diffractometer revealed that beta 1' and gamma 1' phases were found in Cu83.5Ni3.5Al13 alloy, which is the main alloy, while crystal structure of beta-Nb phase was also found with Nb addition. Likewise, the same phases were determined by SEM-EDX analysis. In addition, the result of Vickers hardness measurements indicated that the hardness value of CuAlNi alloys increased by extent of contribution of Nb.