Effect of thermal aging on physical properties of NiMnGa alloy and the x-ray microtomograph analysis

In this study, the influence of aging on thermal, crystal structure and magnetic properties of Ni-%29,5Mn-%21Ga ferromagnetic shape memory alloys (by atomic percentage) were investigated. Firstly heat treatment was performed to these alloys at 900 º C for 2 hours, then was aging at 300 º C, 400 º C and 500 º C for 1 hour. Transition temperature, thermodynamic parameters, the activation energys of these alloys were found by using a differential scanning calorimetry (DSC). In case of martensite, Crystal structure was determined by X-ray analysis device. The physical properties measuring set (PPMS) was used to investigate of the magnetic properties of aged alloys. As a result of experimental studies, it was found that to increase of the transition temperature by aging. The highest transition temperature value was apeared in alloy which was subjected to aging at 300 º C. As for Enthalpy and Entropy variations were increased with the aging temperature in a linear. In all cases, the crystal structure of alloys; peaks which belong to the NM martensite phase and ? -phase were detected from the x-ray analysis. In addition, the highest X-ray intensity was observed in alloy which aging at 300 º C. The highest saturation value of PPMS measurements were detected in alloys which were exposed to aging at 300 º C again. According to these measurements, on thermal, crystal structure and magnetic properties of Ni-%29,5Mn-%21Ga alloys were found to be the effect of aging.Key Words: NiMnGa Alloys, Ferromagnetic shape memory alloys, Heat treatment