Inivestigaiton of effect of heat treatment and alloying element on phyisical properties of Ni-Mn-Ga ferromagnetic shape memory alloy

In this study, the effect of alloy content and heat treatment on physical properties of Ni%29Mn-%21Ga, Ni-%29,5Mn-%20Ga, Ni-%28,5Mn-%20,5Ga and Ni-%29,5Mn-%21Ga (by atomic percent) ferromagnetic shape memory alloys represented by S1, S2, S3 and S4 respectively were investigated.X-ray analyse system was used for determining the crystal structure in martensite case, optic microscope and SEM was used for the investigation of surface morphology, differential scanning calorymetry (DSC) was used for determining the martensite-austenite transformation temperatures, thermodynamic parameters and activation energy of alloys with and without heat treatment. Differential thermal analysis system (TG/DTA) was used to determine the phase transition at high temperature and also the Curie temperature where the transition from ferromagnetic to paramagnetic occured. Physical property measurement system (PPMS) was used to determine the magnetic properties by appling an external magnetic field. According to experimental results obtained the NM and ? phase were seen together, x ray diffractograms, optic microscop and SEM photographs were matched well. Nickel content was sequenced as S3>S2>S1>S4 by weight and there was an linear relation between this sequence and transformation temperature, transformation temperature was increased with a little increase of Nickel content. Furthermore, it was observed that the martensite transformation temperatures were changed with the heat treatment. According to PPMS measurements the highest saturation and coercivite value were obatined at 1000 ºC heat treated alloys according to PPMS measurements.As a result of these measurements, it was concluded that contents of elements and heat treatment temperature had a significant effect on physical properties of NiMnGa alloys and the alloys in same element contents will have same physical properties with the alloys in different element contents by applying only heat treatment cycle.Key Words:NiMnGa Alloys, Ferromagnetic shape memory alloys, Heat treatment, Nonmodulated martensite Structure, Saturation, Coercivite.