Investigation of the effect of pressure on characteristic transformation temperatures in copper-based shape memory alloys

In this thesis, the structural and thermal effects of the samples were investigated by applying pressures at different values of the triple shape recall alloy with melting composition of 82,03 Cu - 13,46 Al - 4,51 Ni (% at.) composition. XRD (X-ray diffraction), DTA (differential thermal analysis), optical microscope observations and DSC (Differential Scanning Calorimetry) analysis methods were used in the analyzes. X-ray diffraction method was used to investigate the crystal structures in the specimen subjected to different pressures and the planes giving rise to the diffraction. Specimen were examined by observing whether martensite structures were formed under room temperature in samples subjected to different pressures under observation of optical microscope. Phase transitions and gradients at high and low temperature ranges of samples subjected to differential pressure by differential thermal analysis have been investigated.The change of temperature parameters (𝐴𝑓, 𝐴𝑠, 𝑀𝑓 and 𝑀𝑠) of austenit-martensite transformations by differential scanning calorimetry method was investigated by the effect of pressure. By the methods applied; it has been determined that the crystal structure of the specimens subjected to different pressures as the result of X-ray diffraction analysis is the orthorhombic structure. The parameters (a, b and c) of the crystal structure were determined by the determined calculations and the changes in the samples were examined by applying different pressures. Crystal dimensions of specimens subjected to differential pressure by the Debye-Scherrer method are found. Observation of optical microscope showed that samples with different pressures were colored and colorless images were taken and it was observed that the formation of martensite in the samples decreased with increasing pressure and martensite was not formed in the sample with 1120 MPa pressure. Phase transitions were investigated by means of differential thermal analysis and it was investigated that these phase transitions were A2 → B2 → 18R or A2 → B2 → 𝐿21 → 18R. It has been observed that there is no transition at pressure applied to 1120 MPa. The phase temperatures of austenite-martensite transformations were investigated by differential scanning calorimetry measurements. Increase of the applied temperature was observed by increasing the pressure applied to the specimens, but at the 560 MPa pressure sample the desired increase of the welded transformation temperature was not observed since the crystal grain size was large. No transformation was observed at the 1120 MPa pressure applied sample.