Abstract-Results of studying structural and phase transformations that occur in the cast high entropy equi atomic AlCrFeCoNiCu alloy after ultrarapid quenching from the melt in an inert atmosphere (RQM) and var ious isothermal treatments are presented for the first time. The investigations have been performed using ana lytical, transmission and scanning electron microscopy, energy dispersive X ray spectroscopy, and X ray diffrac tion structure and phase analyses, as well as measurements of the nanohardness, microhardness, and elastic moduli. It has been found that an ultrafine grained structure is formed in this alloy during RQM. Already during quenching and, especially, during subsequent annealing, the alloy undergoes decomposition, which is accom panied by the precipitation in the bcc (B2) matrix of some nanosized phases, predominantly of equiaxed mor phology, both atomically ordered (B2) and disordered (A2), with various chemical compositions. All nanophases are multicomponent solid solutions and are enriched in a few elements, which leads to a pro nounced nanomodulation of the elemental and phase compositions over the alloy bulk, identified, in particular, from the presence of satellites in the vicinity of some reflections in selected area electron diffraction patterns.
The nanostructured TiNi-based shape-memory alloys were synthesized by severe plastic deformation (SPD), including high pressure torsion, equal-channel angular pressing, and multi-step SPD deformations (SPD plus cold rolling or drawing). It is found that the SPD processing changed the morphology of the martensite and temperature of martensite transformation. Also, we found that the mechanical and shape memory properties can be enhanced by forming nanostructures in these alloys. SPD processing renders higher strength, higher yield dislocation strength and in results-higher recovery stress (up to 1.5 GPa) and maximum reverse strain (up to 10%) of shape memory, which are desirable in various practical application.
Electrical, magnetic and galvanomagnetic properties of half-metallic Heusler alloys of Co2YZ (Y = Ti, V, Cr, Mn, Fe, Ni, and Z = Al, Si, Ga, Ge, In, Sn, Sb) were studied in the temperature range 4.2-900 K and in magnetic fields of up to 100 kOe. It was found that varying Y in Co2YZ alloys affects strongly the electric resistivity and its temperature dependence ρ(T), while this effect is not observed upon changing Z. When Y is varied, extrema (maximum or minimum) are observed in ρ(T) near the Curie temperature TC. At T ≤ TC, the ρ(T) behavior can be ascribed to a change in electronic energy spectrum near the Fermi level. The coefficients of normal and anomalous Hall effect were determined. It was shown that the latter coefficient, RS, is related to the residual resistivity ρ0 by a power law RS ~ ρ0 k /MS with MS the spontaneous magnetization. The exponent k was found to be 1.8 for Co2FeZ alloys, which is typical for asymmetric scattering mechanisms, and 2.9 for Co2YAl alloys, which indicates an additional contribution to the anomalous Hall effect. The type of the temperature dependence ρ(T) is analyzed and discussed in the frame of two-magnon scattering theory.
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