By electric spark dispersion were produced for the first time ultrafine powders (up to 5 mu m) of high-entropy alloy (HEA) FeNiCoCrCu in various liquid media (ethanol, propanol, and water), and their effect on the phase composition and the ratio of the volume fractions of gamma(1) and gamma(2) phases was determined in comparison with this ratio in the original ingot. According to the analysis of the structure parameters and characteristics of the hyperfine magnetic interaction, as shown, the obtained powders inherit the phase composition of the cast alloy, but the formation of the b.c.c. phase, as well as simple and complex oxides after dispersion in ethanol and water, and dispersion in propanol also causes a change in the ratio gamma(1) i gamma(2) phases and the appearance of special carbides. The results are the basis for the development of a new method for obtaining highly dispersed and nanosized HEA powders.

Ультразвуковим обробленням у кульовому млині (УЗКМ) крупнозернистих порошкових сумішей (КЗПС) алюмінію, заліза, кобальту, міді, нікелю та хрому вперше одержано високодисперсні порошки високоентропійних стопів системи AlCoCrCuFeNi та досліджено вплив вмісту алюмінію і хрому на їхній фазовий склад та магнетні властивості

For the first time, ultrafine powders (UFP) of high-entropy alloys (HEA) of the AlCoCrCuFeNi system are produced by ultrasonic milling of the coarsegrained powder mixture of aluminium, iron, cobalt, copper, nickel and chromium in a ball mill. X-ray analysis, Mossbauer spectroscopy and magnetic measurements shows that the phase composition and magnetic properties of UFP are affected by the aluminium and chromium contents. These investigations have shown that all UFPs produced by ultrasonic milling are in highentropy state and contain two solid solutions with f.c.c. and b.c.c. lattices. Both the quantity of b.c.c. phase and magnitude of specific saturation magnetization of UFPs depend on the aluminium and chromium contents in the original powder mixture. Ferromagnetism of the obtained UFPs is shown to be mainly due to the presence of b.c.c. phase.

УкраїнаМета роботи полягала у побудові відсутньої на сьогодні фізико-механічної моделі процесу циклічної гідроекструзії.Представлена модель створена на підґрунті сучасних уявлень механіки і фізики металів про принципи й закономірності росту та релаксації напружень у вершинах концентраторів, не тільки завжди присутніх всередині

The influence of hydroextrusion on structural changes in Invar high-carbon alloy 1N31 with a graphite component has been studied by metallography, microhardness measurements, and transmission electron microscopy. This process is accompanied by an almost twofold increase in microhardness up to a depth of 270–300 μm measured along scratches applied across the longitudinal section of the sample in the last cycle of the second hydrodynamic extrusion pass. It has been proved by means of transmission electron microscopy that the achieved strengthening of the near-surface layers is connected not only with additional solid-solution strengthening of austenite owing to a complete dissolution of the graphite component in it, but also with the extreme dispersion level of structural elements that form twin orientations in two mutually normal directions. The results are discussed in the scope of the model proposed earlier for the formation and features of the hydrodynamic state of the sample material in the course of hydrodynamic extrusion.

The effect of cold plastic deformation by upsetting (e = 1.13) on structure and hybridised bonds of carbon in the fcc Invar Fe-30.9% Ni-1.23% C alloy was studied by means of X-ray phase analysis and X-ray photoelectron spectroscopy. Carbon precipitates along grain boundaries and inside of grains in the alloy after annealing and plastic deformation were revealed. The presence of mainly sp(2)- and sp(3)-hybridised C-C bonds attributing to graphite and amorphous carbon as well as the carbon bonds with impurity atoms and metallic Fe and Ni atoms in austenitic phase were revealed in the annealed and deformed alloy. It was shown for the first time that plastic deformation of the alloy results in partial destruction of the graphite crystal structure, increasing the relative part of amorphous carbon, and redistribution of carbon between structural elements as well as in a solid solution of austenitic phase.

The ultrafine powder of the Heusler Cu-13,1Mn-12,6Al (wt.%) alloy produced by electrical spark dispersion (ESD) in ethanol and the pellets prepared by pressing of the powders and aged in various gas environment (air, Ar, vacuum) were studied by XRD, nuclear magnetic resonance, magnetic and electric transport methods. The constituent phases were identified as b.c.c. α–Cu–Mn–Al, f.c.c. γ-Cu–Mn–Al, Cu2MnAl, and oxides. The sizes of the coherently scattering domains (CSD) and the saturation magnetizations were in the range of 4–90 nm and 0–1.5 Am2/kg, respectively. 27Al and 63Cu NMR spectra of the powders and pellets have shown hyperfine structure caused by contributions from atomic nuclei of the constituent phases. The aging of pellets in different gas environments had effect on their phase composition but no effect on dispersion of the phases. In contrast to the as-cast alloy, electrical resistance of the pellets evidenced semiconducting behavior at elevated temperatures due to the presence of metal oxides formed on the surfaces of nanoparticles.

Вплив кристалічної структури на транспортні та магнітні властивості масивних стопів Гойслера Ni 2 MnSn

The effect of cold plastic deformation by upsetting of the carbon‐containing Invar Fe‐30.9 % Ni‐1.23 % C alloy on structure, magnetic and elastic properties was studied by means of X‐ray diffraction and Mössbauer analysis, magnetic and ultrasonic methods. The crystal lattice distortion and additional dissolution of graphite in austenite increase magnetization, hyperfine magnetic fields at iron nuclei, the Curie temperature essentially smearing this phase transition. These changes are caused by weakened interatomic bond in the Invar alloy detected in decreased elastic moduli and the Debye temperature.

Changes in the dimensional and microstructural characteristics of the samples of two invar fcc alloys, Fe–35.0% Ni–0.49% Mn and Fe–30.9% Ni–1.23% C, have been investigated by X-ray diffraction, metallographic, and electron-microscopic methods after upsetting with the logarithmic deformations e = 0.5 and 1.1. It has been shown that the regularities of changes in the macroscopic dimensions of the samples, as well as in the parameters of structural elements, which are presented by coefficients of the shape change after upsetting, are common for both alloys, although they have some distinctions. These distinctions are caused by the presence of a second phase in the carbon-containing alloy, which is concentrated predominantly along the boundaries of structural elements and affects the changes in the size and microstructural characteristics, as well as by a higher density and greater uniformity of the defect distribution.

In a given article, the results of studies of the structure, which is formed during hydroextrusion (HE) with the strain epsilon = 0.45-3.47, and the features of its influence on the hardness and properties of the Fe-35% Ni Invar alloy are presented. As shown, the plastic deformation leads to formation of the textured substructures, size parameters of which vary in proportion to their disorientation and lie within the range of 50-120 nm, while maintaining the much larger structural elements with sizes of 500-2500 nm. Nonmonotonic variation of the elastic microstresses depending on the degree of deformation with a maximum rate of their growth up to the strain of 1.48 and its subsequent deceleration to epsilon = 3.47 are revealed and are explained by the peculiarities of formation of the hierarchy of size parameters of a substructure, disorientation of fragments, and degree of organization of the boundaries between them. Nonmonotonic work hardening of Invar alloys is revealed and is caused by a refinement of the substructure elements with increasing level of elastic microstresses and their dynamical-relaxation processes. Lower and relatively constant values of TCLE for deformed alloy, -0.26.10(-6)--0.73.10(-6) K-1, at temperatures of 200-300 K are determined.

The impact of deformation of Invar Fe-35 % Ni alloy by hydroextrusion at room temperature on structure and its properties was studied. Grinding of grains, the structure fragmentation on 60 nm blocks and continuous increasing microstresses with growing epsilon within the strain range of epsilon = 0.45-3.47 was shown. The multiple extrusion leads to a non-monotonic change of magnetic properties of the alloy (specific magnetization and the Curie temperature) and as a consequence to thermal expansion measured along the direction of the extrusion due to the microstresses growth and their partial relaxation. The hypothesis concerning the microstresses induced change of a balance between ferromagnetic and antiferromagnetic contributions to exchange interspin interaction is supposed.