Highly dispersed powders of Ni50,3Mn30Ga19,7 were prepared by spark-erosion in ethanol, water, and kerosene. Powder particles have mostly spherical shape and broad size distribution, with a maximum around 1 μm. In the as-prepared state, two series of peaks are observed by x-ray diffraction. They are associated with the disordering of two ordered phases, existed in bulk Ni-Mn-Ga: the high-temperature L21 austenitic phase and the low-temperature L10 martensitic one. Annealing decreases the half-width of the peaks and increases the L10/L21 intensity ratio. Magnetically as-prepared powders demonstrate a clear superparamagnetic behavior that changes to ferromagnetic one after annealing. These properties are quite different from the ones of mechanically dispersed powders and rapidly quenched ribbons of the same composition. The spark-erosion conditions, particularly cooling rates up to 109 K/s, lead to the formation of the mixed phase state, much higher atomic disorder, and to the appearance of different types of structural inhomogeneities.

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621.762Correlation between the mechanical properties of porous materials obtained with use of a pore-forming agent, and the pore structures has been studied. It was shown that the larger the pores, the higher the bending strength and elastic modulus. The curve of mechanica properties versus porosity is S-shaped. A theoretical equation has been derived for this curve. The region of the bend in the S curve was established to correspond to the phase transition of the metallic claster from a quasi-three-dimensional to a quasi-two-dimensional structure.

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