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The Heusler compound with the L21 Ni54Mn20Fe1Ga25 structure subject to high-pressure torsional megaplastic deformation was first systematically studied by in situ methods of X-ray phase analysis and transmission and scanning electron microscopy. It was established that the torsional shear deformation at room temperature reduces the polycrystalline structure of the compound to a nanocrystalline and partially amorphous state. It was revealed that, as the pressure increases from 3 to 5 GPa and the degree of deformation increases from 2 to 5 revolutions, total atomic disordering and sequential structural-phase transformation according to the scheme B2(bcc) → A2(bcc) → A1(fcc) occur. It is shown that annealing at a temperature of 570 K and below causes devitrification of the amorphous phase and annealing at a temperature of 620 K and above causes the restoration of the L21 structure. The dimensional effect of suppressing the thermoelastic martensitic transformation is revealed in the nanostructured austenitic L21 alloy with grains smaller than 80 nm when cooled to 120 K. The capability of the thermoelastic martensitic transformation and of the shape memory is restored in a submicrocrystalline ultrafine-grained alloy after its recrystallization annealing at temperatures above 600 K. [ABSTRACT FROM AUTHOR]

Abstract: Studies of structural and phase transformations in the cast and melt-quenched ferromagnetic four-component alloy Ni54Mn20Fe1Ga25 were performed using transmission and scanning electron microscopy and X-ray diffraction, The obtained data have been compared with the results of studies of physical characteristics (electrical resistance, thermopower, magnetic susceptibility, magnetization, and temperature coefficients of linear expansion and relative elongation ΔL/L measured by the method of dilatometry) in the temperature range of 2-870 K. This work has established the effects of quenching on the microstructure, magnetic state, critical temperatures, and specific features of thermoelastic martensitic transformations in the alloy. [ABSTRACT FROM AUTHOR]

The phase composition, structure, magnetic and thermoelastic martensitic transformations, and physical properties (magnetic susceptibility, magnetization, electric resistivity) in multicomponent magnetic Ni 50 − xCo xMn 29Ga 21 alloys (with a Co content of x = 0, 1, 2, 3, and 10 at %) exhibiting a magnetically controlled shape memory effect are studied. The critical temperatures of the magnetic transitions and thermoelastic martensitic transformations are determined. It is shown that the studied alloys in the austenitic state are substitutional solid solutions based on a quasi-ternary L2 1 superstructure (Ni, Co) 50Mn 29Ga 21. [ABSTRACT FROM AUTHOR]

Ni-Mn-Ga based compounds are of great interest due to their magneto- and temperature operated shape memory. To obtain new results on their electronic structure, we studied the low-temperature kinetic properties and the structure of Ni-Mn-Ga alloys at temperatures T≪ T M, T C ( T M is the temperature of the martensitic transition and T C the temperature of the magnetic (Curie) transition, which are both close to room temperature). Ordered (cast) and disordered samples, having a nanocrystalline substructure, were investigated. The galvanomagnetic and electrical properties were measured in the temperature interval from 2 to 80 K and in magnetic fields of up to 15 T. We find that the electrical and the high-field properties of these alloys strongly change due to the transition into the nanocrystalline state. [ABSTRACT FROM AUTHOR]