The ceramic samples fabricated by spark plasma sintering of powder mixtures based on silicon nitride (Si₃N₄) were investigated. The powder mixtures were made by wet chemical methods from commercial α-Si₃N₄ powder (the particle size <5 μm) and Y₂O₃-Al₂O₃ sintering additive (3% to 10% wt.). Sintering was carried out at the heating rate of 50 °C/min and the load of 70 MPa until the shrinkage end. The powder mixtures and ceramic samples were characterized by scanning electron microscopy and X-ray diffraction. The shrinkage of the powder mixtures during sintering was analyzed, and the activation energy of sintering was calculated according to the Young-Cutler model. The density, microhardness, and fracture toughness of the ceramic samples were also measured. All samples had high relative densities (98%–99%), Vickers microhardness 15.5–17.4 GPa, and Palmquist fracture toughness, 3.8–5.1 MPa∙m^1/2. An increase in the amount of sintering additive led to a decrease in the shrinkage temperature of the powder mixtures. The amount of β-Si₃N₄ in the ceramics decreased monotonically with the increasing amount of sintering additive. The shrinkage rate did not decrease to zero when the maximum compaction was reached at 3% wt. of the sintering additive. On the contrary, it increased sharply due to the beginning of the Si₃N₄ decomposition.

The research results of the microstructure and corrosion resistance of Ti and Ti-Al-V Russian industrial titanium alloys obtained by spark plasma sintering (SPS) are described. Investigations of the microstructure, phase composition, hardness, tensile strength, electrochemical corrosion resistance and hot salt corrosion of Ti-Al-V titanium alloy specimens were carried out. It was shown that the alloy specimens have a uniform highly dense microstructure and high hardness values. The studied alloys also have high resistance to electrochemical corrosion during tests in acidic aqueous solution causing the intergranular corrosion as well as high resistance to the hot salt corrosion. The assumption that the high hardness of the alloys as well as the differences in the corrosion resistance of the central and lateral parts of the specimens are due to the diffusion of carbon from the graphite mold into the specimen surface was suggested.

This study investigates the impact of carbon on the kinetics of the spark plasma sintering (SPS) of nano- and submicron powders WC-10 wt.%Co. Carbon, in the form of graphite, was introduced into powders by mixing. The activation energy of solid-phase sintering was determined for the conditions of isothermal and continuous heating. It has been demonstrated that increasing the carbon content leads to a decrease in the fraction of η-phase particles and a shift of the shrinkage curve towards lower heating temperatures. It has been established that increasing the graphite content in nano- and submicron powders has no significant effect on the SPS activation energy for “mid-range” heating temperatures, Q_S(I). The value of Q_S(I) is close to the activation energy of grain-boundary diffusion in cobalt. It has been demonstrated that increasing the content of graphite leads to a significant decrease in the SPS activation energy, Q_S(II), for “higher-range” heating temperatures due to lower concentration of tungsten atoms in cobalt-based γ-phase. It has been established that the sintering kinetics of fine-grained WC-Co hard alloys is limited by the intensity of diffusion creep of cobalt (Coble creep).

This paper reported the results of research into the effect of Equal Channel Angular Pressing (ECAP) temperature and 1-h annealing temperature on mechanical properties, stress-relaxation resistance, and corrosion resistance of austenitic steel AISI 321L with strongly elongated thin δ-ferrite particles in its microstructure. The formation of α′-martensite and fragmentation of austenite grains takes place during ECAP. Ultrafine-grained (UFG) steels demonstrate increased strength. However, we observed a reduced Hall–Petch coefficient as compared with coarse-grained (CG) steels due to the fragmentation of δ-ferrite particles. UFG steel specimens were found to have 2–3 times higher stress-relaxation resistance as compared with CG steels. For the first time, the high stress-relaxation resistance of UFG steels was shown to stem from a internal stress-relaxation mechanism, i.e., the interaction of lattice dislocations with non-equilibrium grain boundaries. Short-time 1-h annealing of UFG steel specimens at 600–800 °C was found to result in the nucleation of σ-phase nanoparticles. These nanoparticles affect the grain boundary migration, raise strength, and stress-relaxation resistance of steel but reduce the corrosion resistance of UFG steel. Lower corrosion resistance of UFG steel was shown to be related to the formation of α′-martensite during ECAP and the nucleation of σ-phase particles during annealing.

Novel IR-transparent ceramics of erbium-doped Lu₂O₃-MgO and Sc₂O₃-MgO composites have been successfully obtained using a combination of glycine–nitrate self-propagating high-temperature synthesis and vacuum hot-pressing methods. Composites have densities greater than 99.5% of those calculated by X-ray diffraction and consist of uniformly distributed submicron grains of magnesium and rare earth oxides. The transmittances of 1.5 mm thick composites are as high as 84.5% and 78.9% at ~5 µm for Er:Lu₂O₃-MgO and Er:Sc₂O₃-MgO, respectively. Both composites are favorable matrices for doping with erbium ions, which exhibit intense luminescence in the visible, near, and mid-IR under relevant excitation. The position of the luminescence bands is similar to Er:Lu₂O₃ and Er:Sc₂O₃ ceramics; the lifetimes of the ⁴I_13/2 state are 8.85 ± 0.1 ms and 5.7 ± 0.2 ms for 3%Er:Lu₂O₃-MgO and 3%Er:Sc₂O₃-MgO, respectively.