Abstract The effect of the terrestrial gravitation field on crystal growth from a solution–melt during spontaneous crystallization is considered, taking into account that the space station (SS) and a laboratory at the Earth, in which the crystallization processes occur, are a noninertial system. It is shown that the specific feature that distinguishes the crystal growth in the terrestrial conditions is the pressure in the melt caused by the supporting force (the Newton third law). This pressure is absent at SS, and this fact leads to an increase in the unit cell of the melt that undergoes the first-order phase transition. As a result, the crystals grown at the SS have larger sizes than the same crystals grown in terrestrial conditions. They also exhibit an excess stress, the value of which is equal to the support pressure, which is absent at the SS. This situation is compared to the experimental data on growing CrSi_2 crystals from a solution–melt in Zn of the Cr–Si–Zn system.

The effect of the terrestrial gravitation field on crystal growth from a solution–melt during spontaneous crystallization is considered, taking into account that the space station (SS) and a laboratory at the Earth, in which the crystallization processes occur, are a noninertial system. It is shown that the specific feature that distinguishes the crystal growth in the terrestrial conditions is the pressure in the melt caused by the supporting force (the Newton third law). This pressure is absent at SS, and this fact leads to an increase in the unit cell of the melt that undergoes the first-order phase transition. As a result, the crystals grown at the SS have larger sizes than the same crystals grown in terrestrial conditions. They also exhibit an excess stress, the value of which is equal to the support pressure, which is absent at the SS. This situation is compared to the experimental data on growing CrSi 2 crystals from a solution–melt in Zn of the Cr–Si–Zn system.

Experimental data obtained in a study of CrSi 2 microcrystals grown under microgravity conditions from a Zn melt in the Cr–Si–Zn system by the mass crystallization method and then placed in terrestrial conditions are presented and analyzed. New properties of crystals of this kind are observed.

Experimental data and their analysis on the study of Cr〖Si〗_2 microcrystals grown in weightlessness from the melt Zn of Cr-Si-Zn system by mass crystallization and placed in earth conditions are presented. New properties of such crystals are found.

AbstractThe formation of the protective and hardening oxide coatings on the surface of the single-crystal sapphire and sintered corundum (ceramics) is studied. Corundum systems with oxide coatings are as yet unknown and our studies are original. The compositions of the coating based on the mixture of Al_2O_3 and B_2O_3 oxides and a technique of their deposition on the samples are worked out. The strength of the samples during the bending test is studied. It is shown that the hardening of several samples achieves ~30% and microhardness (HV) reaches 30 GPa. Basing on the results of an investigation of the significant number of the samples obtained under different conditions, it is concluded that the developed method of the protection and hardening of the corundum products is promising.

The formation of the protective and hardening oxide coatings on the surface of the single-crystal sapphire and sintered corundum (ceramics) is studied. Corundum systems with oxide coatings are as yet unknown and our studies are original. The compositions of the coating based on the mixture of Al2O3 and B2O3 oxides and a technique of their deposition on the samples are worked out. The strength of the samples during the bending test is studied. It is shown that the hardening of several samples achieves ~30% and microhardness (HV) reaches 30 GPa. Basing on the results of an investigation of the significant number of the samples obtained under different conditions, it is concluded that the developed method of the protection and hardening of the corundum products is promising.

Поступило в Редакцию 11 мая 2017 г

We have analyzed the dependences of microhardness H on load P for the surface layers of Armco iron samples with different initial structures, i.e., annealed and after equal-channel angular pressing (ECAP). The microhardness was measured in air after rolling of the sample in helium or nitrogen medium. It has been found that these mediums produce different effects on the H(P) dependences for preliminarily annealed samples compared to those subjected to ECAP. This is due to the differences in their initial defects structures and in the types of binding forces of helium atoms and nitrogen molecules with dislocations, which determine the intensity of their penetration into the surface layer of the samples under investigation. We have obtained curves that describe the release of helium from samples rolled in different mediums and have measured the amount of helium.

The load dependence of the microhardness of polycrystalline aluminum and iron specimens produced by rolling in a nitrogen, helium, or air medium has been investigated. It has been found that nitrogen and helium have different effects on the microhardness of these metals in the low-load range. This difference is associated with the specific features in the intensity of dynamic penetration of nitrogen and helium into the surface layer of aluminum and iron, which depends on the initial defect crystal structure of the metals, as well as on the type of bonding of helium atoms and nitrogen molecules with metal atoms. It has been shown that the effect of the gaseous medium of the rolling on the microhardness manifests itself only in a very thin surface layer of metal specimens, where the microhardness exhibits a size effect, and an increase in the microhardness indentation depth remains unchanged with an increase in the load and does not depend on the gaseous medium of the prerolling of the specimens.

Single crystals of polyelemental rare earth hexaborides with the preset formula La0.5(Ce0.1Pr0.1Nd0.1Sm0.1Eu0.1)B6 were obtained for the first time. Synthesis and crystallization were performed by the solution–melt method in an immiscible Al/Pb system. Step-by-step chemical analysis was made with the aid of a CAMEBAX microprobe. The inclusion of all rare earth metals (REMs) in the hexaboride lattice was proven, and differences in the composition of obtained crystals caused by nonstationarity of the bulk crystallization process were found. The lattice periods of the polyelemental REM hexaborides were found to be smaller than that of hexaboride of lanthanum, the main element of the metal sublattice. The measured microhardness of the new material lies within the range of the microhardness values of hexaborides of all its constituent REMs. Speculations are provided on the peculiarities of the growth mechanism, crystallization, and composition of the obtained crystals.

The so-called crystallization courtyard is investigated that forms in processes of mass crystallization around the Ge and Si crystals and their solid solutions (Ge+Si) during cooling of hypereutectic alloys in the Ge-Al, Si-Al, and (Ge+Si)-Al eutectic systems. For the first time, data on the composition and microhardness of this crystallization courtyard are given and its role is shown as a stopper of cracking in an Al-(Ge,Si) system during rapid cooling after the heating system is turned off. For the first time, it is suggested that a crystallization courtyard forms in all hypereutectic systems (including every system in which the amount of the taken solvent does not correspond to the eutectic point).

The structure, microhardness, and strength of binary directionally crystallized aluminum alloys with 35, 43, 53, 57, and 64 wt % germanium have been investigated. It has been shown that the eutectic microhardness is constant in the composition region under study. The microstrength of primary crystals of the solid solution of germanium in aluminum with the dendrite structure increases with increasing germanium concentration. However, the difference in the microhardnesses of the eutectic and dendrites, which was determined for each of compositions on the same specimen, does not exceed the measurement error. It has been assumed that the change in the strength of the alloy having the composition in the hypoeutectic region is determined by the redistribution of the volume fractions of the eutectic (α-Al and eutectic germanium) and the domains of primary crystals of the solid solution. This dependence can be described by the mixture rule. Above the eutectic composition, the alloy decomposes in a brittle manner; its strength is likely dependent not only on the content of the components, but also on the form and orientation of primary germanium crystals.

Aluminum-silicon alloys (from 8 to 25 wt % Si) have been prepared by directional crystallization of shaped samples by the Stepanov growth at a solidification rate of 103 μm s−1. The dependences of the microhardness, Young’s modulus, internal friction, yield stress, and ultimate tensile stress of the alloys on the silicon content have been studied. It has been shown that the ultimate tensile stress has a maximum, and the yield stress has a kink at 15 wt % Si; the composition corresponds to the eutectic composition at the solidification rate used. The silicon content in the eutectics increases with an increase in the solidification rate. The increase in the ultimate tensile stress is explained by an increase in the volume fraction of the more strength fine-crystalline structure of the eutectics as a result of the decrease in the volume fraction of more plastic dendrites of the primary crystals of the α-Al solid solution. The decrease in the ultimate tensile stress of the hypereutectic alloy is determined by the increase in the volume fraction of brittle primary silicon crystals of various shapes.

During the use of new technology, the formation of a third intermediate layer in the Pb(+Ru)-Zn(+Sn) system is observed in a binary immiscibility gap system. This layer contains all the components of the systems and presumably consists of the mixture of triple eutectic Pb-Sn-Zn with three double eutectics (Pb-Zn, Pb-Sn, and Sn-Zn). It is located between the initial Pb and Zn layers. Its edges from the sides of both Pb and Zn contain RuZn13 crystals formed within the system, which are confined to narrow regions of pure Zn.

For increase in hardness (durability) and fire resistance (stability to melts metals) corundum ceramics on the basis of Al2O3 authors of the present work have suggested to protect for the first time its surface stronger and fire-resistant coverings, for example, from TiB2. In work results of high-temperature diffusion TiB2 in a surface of plates from Al 2O3 are shown. For the first time the method cathodeluminescencium (KL) for identification and a condition of atom Ti after diffusion is used, in for an establishment of its quantity used method X-ray spectrum the microanalysis (RSMA). Durability increase defined a method microindentification by means of a pyramid of Knoop and strength at a bend. Researches have shown perspectivity of hardening of a surface corundum ceramics and use of the above-stated methods for studying of results of diffusion.

For the first time corundum ceramics are treated with an electron beam, and they are also fired at high temperature with surface coatings made from high-melting and refractory compounds, i.e. titanium diboride, boron and zirconium carbides. Coatings are applied with magnetron deposition and a newly developed mechanochemical method. In all cases there is a considerable increase in the microhardness of treated materials and in some cases an increase in bending strength.

The chemical composition of precipitates, the Knoop microhardness of the precipitates and of the matrix of Al–Si–Ge alloys solidified during centrifugation at 7 × g were investigated. The initial content of (Si + Ge) was (10 + 10), (20 + 20) or (25 + 25) at.%. The Knoop microhardness of the ingots varied with height in the ingot. This variation is attributed to sedimentation of Si–Ge during solidification. Chemical analysis showed that the maximum Si:Ge ratio in the precipitates for Al–10 at.% Si–10 at.% Ge alloy was about 92:8, and decreased with increasing Si and Ge content in ingots. The Si:Ge ratio and Knoop micro hardness also varied throughout each precipitate. The composition was constant along precipitates of alloy solidified without centrifugation. A variation in Knoop microhardness along the precipitates was attributed to this composition variation. The variation of the maximum Si:Ge ratio in the precipitates in ingots of different composition solidified with centrifugation is attributed to nonequilibrium conditions of solidification induced by decreased mass transport in the melt adjacent to the growing precipitates. The variation of Si and Ge along the Si –Ge precipitates is created by convection of the melt during solidification with centrifugation.

The possibility of certifying and checking surface hardening of ceramic plates by neutron scattering methods using neutron radiation diffraction (Bragg and small-angle) is demonstrated. The surface hardening of corundum plates by modifying their surface using magnetron spraying and subsequent fusion of the hardened layer using en electron beam has been performed by the authors for the first time.

Anisotropy of Knoop microhardness is measured in different directions within the limits 0–90 and 0–180° with a step in the azimuth of 22.5° in different identified faces of single crystals belonging to different crystallographic syngony of refractory borides, some of which are used as antioxidants in the production of carbon-containing refractories. Single crystals are prepared from Al solution-melts with slow cooling of the system from 1200–1400 to 20°C. Experimental data for polar anisotropy of microhardness with a step in azimuth indicated are obtained for the first time and their qualitative interpretation is provided.

The properties of single crystal samples of Al1.1Be0.6B22, which are characterized by a large number of atoms per unit volume, have been studied at high (1013-1014 Hz) and low (102-105 Hz) frequencies. There is a considerable contribution to the polarizability of this compound due to a shift of the electron shells relative to the atomic nuclei. This accounts for large values of the refractive index—for example, 3.12 ± 0.05 at 0.64 μm—which is a record value for solids in the transparency range. At low frequencies, the dielectric characteristics are determined by the relatively high conductivity of the material, which represents an extrinsic p type semiconductor.