| In order to improve the brittleness and magnetic properties of NiMnGa alloys,. the Ni50-xFexMn34Ga16 (x=0,2,4,6,8,10,12,14,16,18) ribbons were prepared by melt-spun technique by considering the effect of alloying and rapid solidification. The martensitic transformation temperature, crystal structure, microstructure and magnetic properties of melt-spun and annealed ribbons were studied and analyzed by differential scanning calorimetry (DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy spectrum analysis (EDS), transmission electron microscopy (TEM) and vibrating sample magnetometer (VSM).According to DSC measurements, with the increase of Fe content, the martensitic transformation temperatures of both melt-spun and annealed ribbons decrease with the decrease of the electron concentration. Moreover, the post annealing resulted in the reduction of the transformation hysteresis existing in melt-spun ribbons and the enhancement of the martensitic transformation temperatures.Through the room temperature XRD analyses, it was found that the melt-spun ribbons consist of non-modulated martensite when when Fe content is 0-12% and the γ phase appears when Fe content equals to 12%. In annealed ribbons with Fe content of 0-6%, they are composed of non-modulated martensite. As the Fe content up to 8-12%, the non-modulated martensite and the y phase co-exist in the annealed ribbons. The y phase precipitation occurs in advance indicates that the annealing may promote the precipitation of y phase. In ribbons with Fe content of 14-18%, the austenite and the y phase co-exist in both the melt-spun and the annealed ribbons. Due the fact that the atomic radius ratio of Fe is larger than that of Ni, the lattice constand and the lattice volume are modified with the increase of Fe content. For the the martensite, a increases, c decreases and volume V increases.It was found by room temperature SEM, EDS and TEM analyses that in melt-spun ribbons, when Fe content is 0-10%, the ribbons is composed of plate-shaped martensite with the composition close to the nominal composition. In ribbons with Fe content of 12%, there was Fe and Mn-rich y-phase precipitating from ribbons matrix. For the ribbons with Fe content of 14-18%, the austenite co-exist with y phase. In the annealed, the ribbons is composed of plate-shaped martensite when Fe content is 0-6%. The martensite and the y phase coexisted in ribbons with Fe content of 8-12% and the austenitie and the y phase co-exist in the ribbons with Fe content up to 14-18%. TEM studies showed that there are 4 types of non-modulated martensite plate in ribbons and each plate consists of 2 twin-related variants. The inter-variant interface is coherent {112} twin interface, whereas the inter-plate interface is not coherent interface.M-T curves and the magnetic hysteresis loops of ribbons tested by VSM, it was found that, the martensite in ribbons transformas from antiferromagnetic (or paramagnetic) to ferromagnetic with the increase of Fe content at room temperature, y phase and austenite showed ferromagnetism. And the Curie temperature increases gradually. The saturation magnetization increases as a function of Fe content when Fe content is 0-12% for both the melt-spun and the annealed ribbons. In melt-spun ribbons with Fe content higher than 14%, saturation magnetization decreases with the increase of Fe content, whereas the saturation magnetization is almost the same in annealed ribbons with Fe content higher than 14%. In melt-spun Ni3gFe12Mn34Ga16 ribbon, 1T magnetic field may induce the increase of ～4-10K on the martensitic transformation temperatures with respect to those at the field of 200G, whereas magnetic field intensity has almost no influence on the magnetic transition. |
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