Russian Metallurgy (Metally)最新文献

The effect of vacuum ion-plasma treatment conditions on the surface layer structure of a preliminary strengthened pseudo-β Ti-5553 titanium alloy is studied. During nitriding, the structure comprising titanium nitrides and an interstitial nitrogen solid solution in α titanium is found to form in the modified layer. Vacuum ion-plasma nitriding is shown to increase the microhardness of the surface of Ti-5553 alloy samples from 430 to 650 HV_0.05, i.e., almost 1.5 times as compared to that of the state after strengthening heat treatment. The application of the TiN titanium nitride is noted to increase the microhardness by 2 times, namely, to 910 HV_0.05, whereas a combination of two methods (nitriding and titanium nitride deposition) increases the microhardness to 890 HV_0.05.

The coating based on the MoSi₂–MoB–HfB₂ system on the substrate of the C/C–SiC composite is prepared by the in situ reaction synthesis using the slurry-roasting deposition of the powder composition at 1620°C under an argon expansion pressure of ~1 Pa. The reaction mechanisms in the Mo–HfSi₂–SiB₄–C system predetermining the synthesis of secondary phases MoSi₂, MoB, HfB₂, and HfC are proposed. Thermodynamic calculations of possible chemical reactions are performed. Probable causes for a high porosity of the prepared coating are analyzed.

The structure, morphology, and hardness of the CeO₂ surface layer formed on a Ti–29Nb–13Ta–4.6Zr alloy plate by magnetron sputtering at different process parameters are studied. Under the chosen conditions, a CeO₂ layer having the stoichiometric composition (with the fluorite-type structure, space group Fm(bar {3})m) is found to form. We detected a linear dependence of the surface layer thickness on the sputtering time and an extreme (with a maximum) power dependence of the thickness. As the thickness increases, the decrease in the hardness of the CeO₂ layer is noted. At low coating thicknesses (to 720 nm), the formation of a TiO₂ sublayer is observed.

Abstract—The functional characteristics of high-entropy alloys, in particular, their corrosion properties, are the subject of active study by many scientific groups. The interest in high–entropy alloys is due to their relative ease of production (most often by electric arc melting at low cooling rates), corrosion resistance, and high values of mechanical properties (hardness, strength). A special place among high-entropy alloys is occupied by compositions based on aluminum and transition metals (nickel, iron, cobalt) due to their functional characteristics commensurate with some bulk amorphous compositions. Information on the features of corrosion processes in them is required for a wider industrial application of such alloys. In this work, the corrosion behavior of Al₂₀Ni₂₀Co₂₀Cu₂₀Zr₂₀ alloy is studied in an aqueous 5 wt % NaCl solution at a temperature of 25°C during 1500 h. The alloy is found to be subjected to minimum corrosion due to the dissolution of nickel and cobalt at a corrosion rate of 2.98 ± 0.01 mg/(m² h). Electrochemical measurements demonstrate that the corrosion potential is –0.19 V relative to the Ag/AgCl reference electrode, and polarization into the anode region leads to selective dissolution of nickel and cobalt.

Abstract—The possibility of deposition of an Al–Zr–V–Nb coating in the form of a powder with a fraction of 0.063 mm and a humidity of 0.33%, which are measured using an AND MX-50 device, on a substrate made of 08Kh18N10 steel is considered. The deposition was carried out using a laser installation consisting of an LS-5 laser radiation source and a KUKA KR-60 ha robot in a protective argon atmosphere. Gas blowing was carried out 0.3 s before deposition and 1 s after it. For reliable bonding of the coating powder (Al–Zr–V–Nb) with the surface of the base material (08Kh18N10 steel), a mixture of powder with polyvinyl alcohol is applied onto the steel before melting. According to the data obtained on a Carl Zeiss EVO 40 scanning electron microscope, the optimum conditions of Al–Zr–V–Nb powder deposition on the base material corresponds to a power of 250 W, a processing speed of 0.5 m/s, and a coating thickness of 0.6 mm. At a lower power of 230 W, the coating cannot melt qualitatively; as a result, insufficient melting of the base metal by the coating metal (adhesion) occurs and partial separation takes place. If the power is increased to 270 W, the base and coating materials interact with each other well and create a high-strength coating monolayer, just as that under the optimum conditions. However, cracking occurs and microcracks appear during cooling because of a significant difference in the cooling rates (08Kh18N10 steel plate does not have time to cool at the rate of the coating material). Thus, there is a need to further increase the number of passes or to perform additional melting to create a reliable coating with no discontinuities and islands. Vickers microhardness (HV) measurements during the deposition of an Al–Zr–V–Nb coating demonstrate an increase in HV by more than two times compared to the base material, which is a sufficient reason for using an Al–Zr–V–Nb powder as a strengthening coating for 08Kh18N10 steel.

Abstract—An experimental coating, which is formed during plasma synthesis of tungsten borides and the reduction of metallic tungsten from a mixture based on a scheelite concentrate and boric acid, is studied. The coating is formed on an Al₂O₃ substrate. The step-by-step formation of borides on the substrate surface and the reduction of metallic tungsten using an electric arc plasma generator built in an experimental high-temperature synthesis facility is described. The coating on the substrate consists of reduced metallic tungsten and its borides synthesized in one technological stage during condensation from a dispersed vapor–drop state. To conduct a series of experiments, we designed a prototype of an indirect-acting plasma generator to generate an electric arc plasma flow with a specific power g > 10⁴–10⁵ W/cm². The mixture is destructurized and then sublimated in the form of a vapor–drop phase during the action of a high-temperature plasma flow on the complex structures of the mineral concentrate and its constituent tungsten oxide. Tungsten borides are synthesized during chemical transformations when a dispersed material is removed from a heated plasma flow, nucleation phases form, and the vapor–drop phase condenses on the substrate surface. The synthesis is also accompanied by significant boron sublimation from compounds, which leads to the reduction of metallic tungsten. The material formed during plasma synthesis forms a W–B system and structures, the physicochemical properties of which depend on the composition of the mixture, the flow density, and the plasma pressure and temperature. The results of chemical analysis of the particles forming the W–B coating as a solid solution of dendrites on the Al₂O₃ substrate surface are presented. Using electron microprobe analysis, we determined the phase composition of the coating and revealed the presence of tungsten borides W₂B₅, WB₂, W₂B, and WB and metallic tungsten. The results of producing W–B coatings or films using mineral multicomponent raw materials can be useful in various high-tech industries, including the hydrometallurgical or chemical industry.

The surface and internal defects of long cast rods made of a near-eutectic 84KKhSR Co alloy using nondestructive testing methods, namely, X-ray computed tomography and metal magnetic memory, and macrostructural and fractographic analyses are analyzed. The main defects in the rods are found to be gas pores and cavities. Zone melting is shown to eliminate these defects. Deep pores and cavities are eliminated during the first remelting, and the second remelting leads to complete elimination of defects and stabilization of geometric dimensions along the rod length.

Abstract—The electrochemical behavior of zirconium ions in melts based on alkaline metal fluorides is studied. The kinetic patterns of the electroreduction of zirconium and aluminum from the KF–AlF₃–Al₂O₃–ZrO₂ melts at 750°C are studied by cyclic chronovoltammetry (CV). The influence of the additive content and potential sweep rate on the kinetics of the cathodic process in the melts under non-steady-state conditions is studied. The cathodic discharge currents of aluminum ions are shown to appear in the potential range from –1.6 to –1.7 V relative to the CO/CO₂ electrode potential, and a doubled peak (Al) appears at the potential about –1.9 V, which is associated with aluminum electroreduction from different electroactive ions (({text{A}}{{{text{l}}}_{{text{2}}}}{text{OF}}_{6}^{{2 - }}), ({text{AlF}}_{4}^{ - })). The presented dependences are consistent with the earlier obtained results of measurements in the KF–AlF₃–Al₂O₃ melts. When ZrO₂ is introduced into the KF–AlF₃–Al₂O₃ melt, a plateau and a discharge peak of electroactive ions appear on the cathodic branch of the CV curves at potentials of –1.4 and –1.7 V, respectively. The presence of two responses is associated with the electroreduction of zirconium ions (platform Zr) and the combined electroreduction of zirconium and aluminum ions (peak Al + Zr) with the formation of the intermetallic compound AlxZr. The electroreduction of zirconium ions at more positive potentials is explained as follows. Of the electroactive ions ({text{ZrF}}_{6}^{{2 - }}) and ({text{A}}{{{text{l}}}_{{text{2}}}}{text{OF}}_{6}^{{2 - }}) present in the melt, the former has the lowest bonding energy, while zirconium has a higher carbon affinity compared to aluminum at the experimental temperature. Therefore, the depolarization during the electroreduction of zirconium ions on glassy carbon (GC) is higher.

A numerical model is developed to reveal the distribution of residual stresses during spot welding of aluminum alloys. The character of fracture of the welded joint during cyclic loading is shown.

Abstract—The effective viscosity (viscoelasticity) of cesium–borate melts has been measured in the temperature interval 900–1600 K at Cs₂O concentration x varying from 0 to 16 mol % by the method of vibrational viscometry. It has been shown than vibration causes a non-Newtonian flow of melts. This means that the activation energy of viscous flow is related not only to the configuration activation energy (the switching energy of oxygen bridge bonds) but also to the elastic energy of structural units in the melt. Using the parameters of Newtonian and non-Newtonian flows, shear viscosity η', elasticity modulus G ', and storage viscosity η" have been calculated. It has been found that in the case of high shear rates, cesium–borate melts may be considered as fluids with viscous and elastic properties. Glass transition temperature T_g has been determined by the differential scanning calorimetry method, and its dependence on cesium oxide concentration has been explained.