Metallurgist最新文献

The results of structural studies and assessment of the bending strength of a VKNA-4U alloy based on nickel aluminide are presented. It is for the first time that this alloy was produced by spark plasma sintering of mechanically activated powders of the starting components. The mechanical activation of the powders lasted for 1.5, 3.5, and 5 min. X‑ray diffraction analysis was performed to determine the optimal duration (3 min 30 sec) of mechanical activation for this alloy. To obtain a dense low-defect workpiece, the VKNA-4U alloy was sintered at a heating temperature of 1100 °C, a pressure of 40 MPa, and a holding time of 5 min. This material has higher ultimate bending strength at room temperature (σ_bend = 1215 ± 65 MPa) than the strength of Ni₃Al intermetallic compound produced in similar conditions and microhardness 690 ± 25 HV.

A method has been proposed to enhance the mechanical properties of hot-finished sintered steels, which consists of additional plastic deformation with a degree of deformation, at which the intracrystalline bonding of the material is preserved. The effect of ultrafine silicon nitride particles on the structural formation and properties of hot-finished sintered steels is analyzed.

The influence of laser welding modes on the structure and properties of butt joints formed for the models of cast sample—cast sample, wrought sample—wrought sample, as well as a hybrid joint of a cast and a wrought sample of Al3Ca0.5La1Mn aluminum-calcium alloy, was studied. The influence of welding parameters on the quality of the weld was evaluated using structural and mechanical tests. The optimal welding parameters were identified as follows: laser power of 1400–1600 W, welding speed of 20 mm/s, focal length of 193 mm, and argon flow rate supplied to the welding zone of 15 L/min. This resulted in the formation of a high-quality welded joint with low porosity and the absence of cracks. The variation in the mass fraction of alloying elements in the process of laser welding of aluminum-calcium alloys was revealed. Under optimal laser welding modes, calcium evaporation in the melting zone is approximately 6.5–10.3%. The obtained joints exhibit a factor of safety of 0.71–0.83 of the ultimate strength of the base metal.

Laser surface alloying is a method used to modify a metal surface to produce a thin surface layer with improved mechanical properties. The results of tests on surface carburizing and boriding of steel 20 using a laser beam are presented. Before laser irradiation, the surface of the material was coated. Two types of coating were used: suspensions of graphite powder and boron carbide. Steel 20 was carburized and borided by melting the coating and the substrate. This processing produced various microstructures in the surface layer, depending on the type of coating used and the processing parameters. The microhardness of the alloyed layers was measured along the depth axis. The surface layer consists of an alloying zone and a heat-affected zone. Some specimens carburized by surface alloying displayed cracking and porosity due to carbon enrichment and high solidification rates. The laser-borated surface has a remelting zone consisting of an eutectic mixture of iron borides FeB, Fe₂B, and Fe₃B. The dense boride zone located near the surface, while the content of the eutectic mixture of borides and martensite increased toward the base metal. The microhardness of the borated layer was 1200 HV. The alloy layers were tested for abrasive wear.

The article presents a method for increasing the operating time of a cyclic unit by combining the operations of torch and gas-dynamic gunning through addition of magnesium briquetted flux.

At present, the available data on the behavior of osmium in the course of extraction of rhenium from washing sulfuric acid used in the production of copper are extremely limited and contradictory. In this connection, the investigation of its behavior in some processes of processing of osmium-containing raw materials and its purposeful accumulation in cruds prove to be quite urgent. We formulate possible causes of formation of the interphase suspensions (in what follows, referred to as cruds) in the technology of rhenium extraction. We also present the results of investigations aimed at the development of physical and chemical foundations of the processes of getting osmium concentrates. A technology of crud processing based on the processes of repulping, sintering, leaching, and extraction of rhenium is proposed. The optimal conditions for the main operations are studied and selected: for repulping, these are S:L = 1:5 with stirring for 1 h at room temperature; for sintering, the consumption of CaO is 200–300% (1:3) relative to the weight of the sediment, its temperature is 300 °C, and the duration of sintering is 2 h, and, for leaching of the cake, S:L=1:4 at a temperature of 20–40 °C for 1 h. We propose a combined method for the extraction of osmium into a concentrate. This enables us to concentrate osmium in the cake and then use this cake to obtain metallic osmium. In this case, a significant part of rhenium (93%) remains in the solution and is then sent to the operation of getting ammonium perrhenate.

In this work four metal powder compositions of VZL718 (IN718) alloy are produced, one by vacuum induction melting and gas atomization (VIGA) technology and three by plasma melting and rotating billet centrifugal atomization (PREP) technology. Their particle size distributions, distribution parameters, technological properties, moisture content and gas impurity content of VIGA and PREP initial metal powder compositions are investigated. The differences between VIGA metal powder compositions and PREP metal powder compositions are shown and analyzed, and the differences are explained. Four selective laser melting processes are conducted using the VIGA and PREP metal powder compositions investigated. Particle size distributions, distribution parameters and process characteristics of VIGA metal powder compositions and PREP metal powder compositions after a single application in a selective laser melting process are investigated, and the differences between changes in characteristics and particle size distributions of VIGA and PREP metal powder compositions are revealed. The reasons for the changes identified in VIGA metal powder compositions and PREP metal powder compositions after selective laser melting and the relationships with initial metal powder composition characteristics are explained. Derivations and conclusions about further possibility of reuse of VIGA and PREP metal powder compositions after selective laser melting are made.

The study investigated the effect of retrogression and re-aging (RRA) on the structure and properties of the new Al–3.5Zn–3.5Mg–3.5Cu–1.6Er–0.2Zr–0.2Cr alloy through the use of scanning electron microscopy, thermodynamic calculations, hardness tests, current density, and corrosion potential. During the crystallization process, chromium is distributed between primary intermetallic compounds with an approximate composition of (Al,Zn)_79.8Mg_4.7Cu₃Cr_5.5(Er,Ti)₇, with a size of approximately 10 μm and an aluminum solid solution. Following two-stage homogenization heat treatment, the Al₈Cu₄Er and Mg₂Si phases exhibit minimal morphological changes, with the θ‑phase (Al₂Cu) being completely dissolved and the T‑phase (Al,Zn,Mg,Cu) transformed into the S‑phase (Al₂CuMg). Thermodynamic calculations indicate that the alloy should also contain the Al₃Zr and Al₄₅Cr₇ phases, which precipitate from the supersaturated solid solution during homogenization. Age hardening in the temperature range of 150–210 °C occurs due to the release of metastable modifications of the T‑phase. The combination of hardness (140 HV) and corrosion resistance (minimum corrosion current density 1 μA/cm²) is optimized by retrogression and re-aging.

The article provides results of research on layer-by-layer plasma surfacing of aluminum alloy AMg5 using vertical supply of de-energized filler wire for product additive formation. Metallographic studies and mechanical tests of surfaced metal are conducted. The metal obtained has a homogeneous structure without defects and has mechanical properties close to those of material prepared by traditional technologies.

For the first time pilot castings of an aluminum alloy into a patented mold with an evaporative-condensation cooling system are carried out with extraction of the resulting cylindrical billet obtained with a diameter of 62 mm. It is shown that the flow rate of cooling water to a mold may be reduced by a factor of 2–3 by increasing the temperature of the water leaving the condenser to t = 60–80 °C. Adjustments are made to the design calculation of wall temperatures, taking into account preliminary heating of the crystallizer and experimental values of temperatures. The state of the surface of the workpieces obtained is analyzed in two pouring modes. Calculation and comparison of heat supplied to and removed from the mold, and thickness of a billet skin are performed.