Effects of cu doping on the physical properties of niti based shape memory alloys

SUMMARY EFFECTS OF CU DOPING ON THE PHYSICAL PROPERTIES OF NITI BASED SHAPE MEMORY ALLOYS In this study, shape memory characteristics of NiTiCu alloys prepared by adding Cu (copper) to NiTi shape memory alloys at different ratios, were investigated. Phase transformation temperatures of the alloys produced in this study, Ni-50Ti, Ni-% 45Ti, Ni-% 55Ti, Ni-% 50Ti- 5Cu and Ni-% 45Ti- 10Cu, were determined by differential scanning calorimetry (DSC). According to DSC results, it was observed that phase conversion temperatures of the alloy Ni-% 55Ti dual shape memory were the highest. It was determined shape memory effect of the 10% Cu added triple NiTiCu was disappeared. The activation energy values of the samples were determined as 155.63 kJ / mol, 226.47 kJ / mol, 207.3 kJ / mol and 101.15 kJ / mol for the alloys Ni- 50% Ti, Ni- 45% Ti, Ni- 55% Ti, Ni- , 84 kJ / mol, respectively. It can be said that with the increasing titanium ratio activation energy of the alloy increases. Besides, it can be said that the addition of 5% Cu to NiTi alloy greatly reduces the activation energy required for transition from the Martensite phase to the Austenite phase. In addition, X-ray, SEM and optical microscope observations were performed in order to determine the structure. Martensite plates were not observed in SEM and optic micrographs because Ni- 50% Ti and Ni-% 45Ti alloys were in austenite phase at room temperature, but micrographs of Ni-% 55Ti, Ni-% 50Ti- 5Cu alloys revealed martensite platelets in some places. XRD measurements taken at room temperature also revealed peaks of the B19 / and B2 phases representing very little martensite phase for Ni- 50% Ti and Ni-% 45 Ti alloys. In Ni-55% Ti and Ni-50% Ti-5% Cu alloys, increased numbers and intensity of the martensite peaks were observed. Keywords: Cu- based shape memory alloys, Cu-Ni-Ti alloys, phase transformations, transformation temperatures.