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Investigations of plastic deformation of fine-grained ceramics based on alumina obtained by the method of spark plasma sintering in the temperature range of 1150-1320 ° C at an applied stress of 40-100 MPa are presented. Based on the experimental data, the parameters of rheological equations were established. It is shown that the mechanism of high-temperature deformation of alumina is superplasticity. In the process of plastic deformation, the grains of alumina do not stretch, which confirms the mechanism of superplasticity - grain boundary sliding. The activation energy for superplastic deformation was Q = 17.8 kTm at d = 6 μm and Q = 24.6 kTm at d = 1 μ m, which is very close to the activation energy of grain boundary diffusion in aluminum oxide Qb = 20 kTm. For a coarse-grained material, an assumption was made about a possible mechanism for lowering the activation energy due to the generation of dislocations by the grain boundary.

The results of studies of the kinetics of high-speed spark plasma sintering (SPS) of plasma-chemical nanosized and industrial micron tungsten carbide powders are described. During SPS the carburization of the surface layer of tungsten carbide samples takes place, which leads to differences in the phase composition and hardness of the surface and central regions of sintered ceramics. The process of SPS of tungsten carbide can be sequentially represented as a change of the following mechanisms: rearrangement of particles at lower temperatures (Stage I) → sintering of particles due to grain boundary diffusion (Stage II) → sintering due to diffusion in the crystal lattice (Stage III- 1) → sintering under conditions of intensive grain growth with an abnormally low diffusion activation energy (Stage III-2).

The features of spark plasma sintering (SPS) of plasma-chemical nanopowders with an increased oxygen content are investigated. It is shown that the process of shrinkage of nanopowders during SPS is limited by the rate of grain-boundary diffusion with anomalously low values of the activation energy. It has been established that a decrease in the activation energy of SPS may be due to the effect of oxygen on the diffusion permeability of grain boundaries of tungsten carbide at the stage of intense compaction, as well as anomalous grain growth at the stage of high-temperature sintering. The SPS kinetics of WC-W2C-WO3-W nanopowder compositions at the stage of intensive compaction is controlled by the rate of sintering of oxide particles with their simultaneous transformation into W2C particles, and then, at the stage of high-temperature sintering, by the process of plastic flow of W2C particles in the presence of tungsten particles. Ceramic samples with high density (98-99%), ultrafine-grained structure (average grain size less than 0.3 μm), having increased hardness were obtained by the SPS method. Hv = 30.5 GPa at Palmquist crack resistance ∼ 6.5 MPa · m1/2.

A new method of mechanical testing of high-strength ultrafine-grained ceramic materials by the method of spark plasma sintering (SPS) is proposed. A promising scheme for testing cylindrical SPS-samples is the “Ball on three balls test” (B3B) scheme. The B3B test method has advantages over the standard four-point bending test method, since it is not necessary to cut standard samples from disks, cylindrical samples are aligned on a special support. In this paper, we present a methodology for processing experimental B3B test data developed using the finite element method. The finite element method for estimating the parameters allows us to consider a larger number of parameters that affect the absolute value of the maximum principal stress. The experimental data processing technique takes into account the influence of the sample size, equipment geometry, physical and mechanical properties of the material, and friction coefficient.

The effect of carbon on the kinetics of spark plasma sintering (SPS) of submicron powder compositions WC-10wt.%Co is investigated. Free carbon in the form of graphite was added into submicron powders by mixing. The activation energy of solid-phase sintering under the conditions of isothermal hold and continuous heating rate sintering was determined. It was shown that an increase in the carbon content leads to a decrease in the volume fraction of particles of the η-phase and a shift of the shrinkage curve to the region of lower heating temperatures. It was established that an increase in the graphite content does not significantly affect the activation energy of sintering of submicron powders in the region of “average” heating temperatures, the value of which is close to the activation energy of grain boundary diffusion in cobalt. It has been shown that an increase in graphite content leads to a significant decrease in the activation energy of compaction of WC-Co powders in the region of “high” sintering temperatures due to a decrease in the concentration of tungsten atoms in the γ phase based on cobalt. The kinetics of sintering of fine-grained WC-Co hard alloys is limited by the intensity of the cobalt diffusion creep by Coble.

The paper describes the results of experimental studies of the superplasticity of ultrafine-grained (UFG) high-purity copper, as well as UFG copper alloys Cu-Ag and Cu-Cr. The study shows that the introduction of small (up to 0.1 wt.%) additives of alloying elements leads to an increase in the ductility of UFG copper at elevated temperatures. An increase in the concentration of alloying elements complicates the process of plastic flow of UFG copper at elevated temperatures due to the difficulty in grain-boundary sliding.

A 90WC-10Co powder mixture with TaC, VC and Cr3C2 grain growth inhibitors with average particle size about 50 nm was produced by deposition of Co. Two different sintering techniques had been used for consolidation. Microhardness and fracture toughness measurements of sintered materials had showed agreement with Hall-Petch equation. The corrosion behavior was investigated in neutral and acid solutions by electrochemical methods. The observed pseudo-passive transition had been associated with the so-called salt passivity — formation of cobalt sulfate salt layer on hard alloy surfaces.

The article provides the results of investigation of the way various types of thermal treatment affect the microstructure parameters and mechanical properties of grade 76HF (R65) carbon rail steels produced by Russian and Japanese manufacturers and used for the production of R65 rails. We determined the optimal heat treatment conditions to provide an increased microhardness and wear resistance of rail steel.

This paper presents the results of studying the thermal stability of the grain structure, mechanical properties, and electrical resistivity of the Al-0.5wt.%Mg-xSc submicrocrystalline (SMC) alloys with varying Sc content (x = 0, 0.1, 0.2, 0.3, 0.4, 0.5 wt.%). The SMC alloys were produced by equal-channel angular pressing (ECAP). The alloys with Sc concentration above 0.3 wt.% contained submicron Al3Sc primary particles, the amount of which increased with increasing Sc concentration. High thermal stability of the SMC structure in the alloys was ensured by ECAP at 225 °C whereas the recrystallization onset temperature was 375 °C. The disintegration kinetics of the Al3Sc particles in the SMC alloys was determined by the diffusion intensity along the dislocation cores in the lattice as well as at the grain boundaries.

The paper provides the results of experimental studies of the microstructure, mechanical properties, and corrosion resistance of cast and submicrocrystalline (SMC) aluminum alloys Al-2.5Mg-Sc-Zr with different ratios of scandium and zirconium (Sc + Zr = 0.32 wt.%). SMC structure in alloys was formed by methods of severe plastic deformation: equal-channel angular pressing and rotary swaging. In our paper, we demonstrate that the alloys have high thermal stability – the recrystallization point in SMC alloys is 250-275 °C. We prove that the replacing scandium with zirconium leads to an increase in the thermal stability of the solid solution of scandium in cast and SMC aluminum alloys Al-Mg-Sc-Zr.

The paper describes the results of experimental studies of the effect of small chromium additives on the temperature of recrystallization (TR) of ultrafine-grained (UFG) copper obtained by equal channel angular pressing. Our investigation shows that the process of recrystallization in UFG CuCr copper alloys has a three-stage character - anomalous grain growth at annealing temperatures not exceeding the temperature of chromium particles(Tann1), “fixation” of grain boundaries by the released particles (T1⩽Tann2), and regular grain growth at higher temperatures (Tann⩾T2), when grain boundaries “detach” from particles of the second stage. It also shows that an increase in the chromium concentration in UFG copper by 0.3-0.5wt.% leads to a decrease in the temperature of the onset of the migration of grain boundaries T1 in the UFG copper by 40-60°C and an increase in temperature T2 to ∼ 400°C. We discovered that low-temperature pre-recrystallization annealing contributes to an increase in the thermal stability of the mechanical properties of CuCr alloys.

This work investigated the sintering of the nanocrystalline tungsten carbide and cobalt composite powder. Vacuum sintering and spark plasma sintering (SPS) were used to consolidate powders into bulk nanocrystalline materials. In addition, two methods of the cobalt introduction were developed for making WC/Co compositions. The first one uses mechanical mixing in ball milling machine. The second one is based on a precipitation and reduction of the cobalt salt on the WC particle surface. The oxygen was always present in the produced powders. Therefore, a control of common carbon is necessary to produce bulk materials with correct chemistry. When vacuum sintering or SPS process are used for consolidation, the addition of grain growth inhibitor is necessary to minimize grain growth. Sintering hard alloys using the nanocrystalline WC-Co composite powders has unique properties and potential for commercial applications.