Russian Metallurgy (Metally)最新文献

A hydrometallurgical technology for processing a titanomagnetite concentrate is proposed and substantiated. The technology includes the decomposition of the concentrate in a weakly concentrated sulfuric acid solution in the presence of a sulfonic cation-exchange resin in the H⁺ form with the transition of the major portion of metals of the titanomagnetite concentrate to the sorbent and the formation of an ilmenite-enriched residue; the desorption of metals from the saturated sulfonic cation-exchange resin with a 5 M solution of sodium chloride; the fractional hydrolytic precipitation and separation of titanium hydroxide, iron hydroxide enriched in vanadium, pure iron hydroxide, and a mixture of iron and manganese hydroxides; and the regeneration of the sulfonic cation-exchange resin. The optimum parameters of the particular processes are determined. Sulfuric acid is weakly consumed and no liquid wastes are formed in the technology.

Hard magnetic Fe–30Cr–20Co (wt %) compositions alloyed with to 3 wt % tungsten are obtained by powder metallurgy. The studies of the magnetic properties show that tungsten additions increase coercive force H_c and maximum energy product (BH)_max but decrease remanence B_r. This effect increases as the tungsten content in the material increases. The maximum values of H_c (55.8 kA/m) and (BH)_max (17.2 kJ/m³) are observed for the alloy with 3 wt % W. In this case, the alloys investigated in the present study were found to be sensitive to heat-treatment conditions. According to X-ray diffraction data, the alloys subjected to a complete heat treatment cycle are characterized by the presence of a marked fraction of the nonmagnetic γ phase; however, in this case, the magnetic properties correspond to those observed for analogous as-cast alloys. In the course of compression tests, all compositions alloyed with tungsten fail before reaching a strain of 20%, whereas, under the same condition, the unalloyed Fe–30Cr–20Co (wt %) composition is deformed without failure. Thus, tungsten additions decrease the plasticity of the material.

X-ray diffraction is used to investigate the effect of the tensile strain on the phase composition, texture, and stress state of the α and γ phases in VNS9-Sh alloy. The α phase content increases from 75 to 91% at the surface and from 45–50% to approximately 70% in the subsurface layers during testing until failure. The relative amount of decomposed austenite at different stages of tensile deformation, which reflects the metastability of austenite, is proposed as a parameter to measure the tendency of two-phase steels to the TRIP effect. Compressive stresses up to –1000 MPa form in austenite at the surface in a 0.3-mm-thick initial steel strip due to the positive volume effect of the γ → α transformation. In contrast, tensile stresses are observed in martensite. Heating the metal creates the compressive stresses, but the subsequent cooling causes tensile stresses in martensite because of its lower linear thermal expansion coefficient (LTEC) as compared to austenite.

The influence of pulsed helium ion (HI) and helium plasma (HP) fluxes on an Inconel 718 alloy fabricated by an additive technology via selective laser melting and subsequent heat treatment is studied. The structural changes in the surface layer (SL) after irradiation are analyzed for two different modes: soft (at radiation power density q = 2 × 10⁸ W/cm² and pulse duration τ = 50 ns) and hard (at q = 1.5 × 10⁹ W/cm², τ = 25 ns). The number of pulses in each mode is N = 10 and 20. Both before and after irradiation, the structure of the alloy is found to be a single-phase solid solution based on nickel with an fcc lattice. The action of pulsed HI and HP fluxes on the alloy changes its texture from initial 〈220〉 to the 〈111〉 direction. This texture change promotes plastic deformation in the irradiated SL. During this process, slip occurs primarily along the {111} planes in fcc metals subjected to thermal stresses. The irradiation conditions affect the lattice parameters of the alloy. Soft HI and HP irradiation reduces lattice parameter a as compared to the initial value, which can be caused by residual macrostresses and the evaporation of impurity atoms located in interstitial lattice sites from SL. Hard mode irradiation increases parameter a mainly due to the influence of helium ion implantation, which promotes its growth. The observed structural changes in the SL of the alloy are shown to decrease the microhardness and to soften the remelted layer. A numerical simulation is used to estimate the role of thermal and shock-wave effects in the plastic deformation and the structural changes in SL under the applied irradiation conditions.

The microstructure and mechanical properties (at room and elevated temperatures) of ultrafine-grained (UFG) 08Kh18N10T steel fabricated by equal-channel angular pressing (ECAP) at temperatures of 150 and 450°C are studied. The UFG steel is found to have a high α' martensite content, and σ-phase nanoparticles precipitate in it upon heating. The UFG steel is shown to have a high ultimate tensile strength and good ductility. The Hall–Petch coefficient of the UFG steel is found to decrease due to the fragmentation of δ-ferrite particles during ECAP.

The effect of equal-channel angular pressing (ECAP) at 150°C and subsequent aging on the structure and strength characteristics of Al–Mg₂Si alloys with scandium and joint (Sc + Zr) and (Sc + Hf) additions is studied. Hardness and electrical resistivity curves demonstrate the decomposition of the supersaturated solid solution in the alloys with (Sc + Zr) and (Sc + Hf) additions is found to be same, and the optimum aging conditions of the alloys are obtained. The microstructure of the alloys and precipitation of secondary phases are studied in detail using scanning and transmission electron microscopy (SEM and TEM, respectively). The alloys subjected to ECAP and aging demonstrate an increase in the strength and the plasticity due to compensation of aging processes by recovery processes related to restructuring a dislocation structure.