No 6 (2023)

The possibility of using the fractional precipitation of rare-earth metals (REMs) and manganese from hydrochloric acid solutions by ammonium carbonate is considered. Specific features of the behavior of elements during precipitation, which are necessary to know when preparing selective REM and manganese concentrates, have been revealed. At pH 5.25, 85% ΣTR₂O₃ pass to a deposit (in the oxide formula, ΣTR is the commonly accepted international designation of REMs), and the REM content is 60.5%. At pH 5.25–7.4, 92% manganese are extracted to a manganese concentrate, and the MnO content in the concentrate reaches 70.7%. The complicated chemical composition of the solution requires three-stage fractional precipitation for preparing qualitative selective concentrates: iron and thorium should be precipitated as a cake at the first stage, and REMs and manganese should be precipitated at the second and third stages, respectively. This makes it possible to form deactivated concentrates in the form of carbonates suitable for the further extraction of REMs and manganese by the well-known methods.

Abstract—The influence of annealing at 600°C on the mechanical and thermomechanical characteristics of a Ti₅₀Pd₃₀Ni₂₀ alloy with high-temperature shape memory effect (SME) is studied. The best strength (σ_u = 1030 ± 140 MPa) and plastic (ε0max">ε${\text{ε}}_0^{max}$ = 11.5 ± 6.0%, δ_res = 6 ± 4%) characteristics have been obtained after annealing at 600°C. The maximum thermally recoverable strain (ε_SME = 4.3%) and the maximum degree of shape recovery (η_SME = 67%) are achieved after annealing at 600°C after preliminary induced tensile deformation at temperatures t_d =235–230°C and a strain rate ε˙">ε$\dot{\text{ε}}$ ≈ 2.8 × 10^–3 s^–1; in this case, the reverse martensitic transformation temperatures characterizing the main shape recovery are A_sSME = 220°C and A_fSME = 249°C. Taking into account the studies carried out before, we found that the martensitic transformation temperatures increase almost linearly and, conversely, the SME and the degrees of shape recovery decrease as the titanium nickelide is alloyed with palladium in the content range from 30 to 50 at %. Linear regression equations are derived. The results obtained are used for designing safety devices of, e.g., crosscutting and pushing types.

The deformation behavior of an ultrafine-grained (UFG) 08Kh18N10T steel at elevated temperatures (450–900°C) has been studied. The maximum elongation to failure (~250%) is detected at a temperature of 750°C. The deformation of the UFG steel at elevated temperatures is controlled by the intensities of simultaneous processes of grain-boundary sliding and power-law creep. The contribution of each mechanism depends on the grain growth rate under superplasticity conditions, which affects the rate of defect accumulation at migrating grain boundaries. The fracture of the UFG steel has a cavitation character: the fracture and specimen surfaces after high-temperature tests contain large elongated pores having formed on nonmetallic inclusions and submicron pores having formed on σ-phase particles.

The deformation behavior and microstructural evolution of a Co–28Cr–6Mo alloy during uniaxial compression tests have been analyzed. The tests are carried out at 1000, 1100, and 1200°C and strain rates of 1, 10, and 50 s^–1 using a Gleeble 3800 machine. Deformation resistance curves are obtained and the peak stresses are determined. The deformation behavior of the alloy is characterized by an increase in the flow stress with the strain rate and by its decrease with increasing temperature. The peak stress is recorded at higher strains when the temperature decreases or the strain rate increases. Deformation in the temperature range of 1000–1100°C is accompanied by strain hardening and partial dynamic recrystallization. After deformation at 1200°C, the microstructure of specimens consists of equiaxed recrystallized grains, and the microhardness does not depend on the strain rate. At the same time, an increase in the strain rate at 1000–1100°C leads to a slight decrease in the microhardness. The data obtained can be used for selecting deformation conditions for the Co–28Cr–6Mo alloy using industrial metal forming methods.

The effect of impurities on the structural and physicochemical properties of melts is considered in order to improve the service properties of cast high-temperature alloys. The changes in the state of nickel melts depending on the tin impurity content and the temperature are studied using the parameters of such structurally sensitive properties as density and surface tension. When the tin content in nickel melts increases to several hundredths of a percent, their density and compression effect are found to increase; however, a further increase in the tin content to 0.6 wt % is accompanied by a significant decrease in these properties. A stable nickel-based cluster solution is shown to form when the density and the surface tension increase at 0.02 wt % tin. When the temperature increases to 1650°C, the properties of the melts are characterized by a slight decrease in the surface tension and the density at a retained type of dependences.

Magnetron sputtering and subsequent annealing are used to form nano- and micron-sized cerium dioxide (CeO₂) surface layers on a VT6 titanium alloy base. The structure of samples is studied by scanning electron microscopy, Auger-electron spectroscopy, energy dispersive spectroscopy, and X-ray diffraction analysis. We detected a linear dependence of the surface layer thickness on the deposition time, a nonlinear increase in the thickness with the supply power, an increase in the surface roughness, and delamination and surface layer loosening, which are likely to be related to annealing. For samples with a surface layer less than 750 nm in thickness, the formation of a TiO₂, Al₂O₃, and CeVO₄ sublayer is found; at a layer thickness of less than 300 nm, the entire cerium dioxide is consumed to form vanadate from vanadium dioxide.