Vol 2019, No 5 (2019)

A new process is developed for metallurgical beneficiation of iron laterite nickel-containing (limonite) ores with the formation of a metallic nickel–cobalt concentrate. This process includes reducing roasting of the ores with sulfur-containing additions in the temperature range 1100–1200°C, the fragmentation of the roasting product, and the magnetic separation of metallic and slag phases. The coarsening of metallic particles in roasting is shown to occur with the participation of a low-melting-point phase (iron oxysulfide Fe(O,S)). In this case, nickel and cobalt concentrate in a metallic phase in the form of an alloy with iron (ferronickel). At the optimum charge composition and reducing roasting parameters, ferronickel particles coalesce and grow to 40–100 μm, which creates favorable conditions for the subsequent beneficiation of the roasting product (cinder) by magnetic separation. After wet magnetic separation of a fragmented cinder, the extraction of nickel and cobalt into a magnetic fraction is 92 and 84%, respectively. When a poor limonite ore (1.03% Ni, 0.05% Co) is processed according to the developed technology, the synthesized metallic concentrate contains up to 8.3% Ni and 0.37% Co.

Linear voltammetry in the potentiodynamic mode is used to study the electrochemical behavior of a heavy tungsten-containing VNZh alloy (in wt %: 90 W, 7 Ni, 3 Fe) and its components in ammonia–alkali electrolytes. The anodic oxidation of individual tungsten and nickel is found to be activated when NH₄OH is introduced into the composition of an alkaline electrolyte. Galvanostatic electrolysis is used to perform electrochemical processing of a VNZh-type alloy with a current efficiency of about 100% for tungsten and a specific energy consumption of ~1.5 kW h/kg.

The microstructures of a commercial aluminum foil and an aluminum foil alloyed by 0.001 wt % scandium are studied before and after electrochemical etching. The strength properties, the capacitance, and the weldability of the foils subjected to electrochemical etching are investigated. We are the first to show that the alloying of aluminum by such a low amount of scandium affects the microstructure of a foil and is sufficient for increasing the strength properties, the capacitance, and the weldability of the aluminum foil used for capacitors.

A thermodynamic analysis of the influence of titanium on the oxygen solubility in Fe–Co–Cr melts at 1873 K is performed. The dependences of the oxygen solubility in Fe–Co–Cr melts on the titanium content are calculated. The titanium content at which the deoxidation reaction mechanism is changed (Cr₂O₃ \( \rightleftarrows \) Ti₃O₅) is as follows: 2.602 × 10^–3% Ti for the Fe–10% Co–10% Cr alloy and 2.975 × 10^–3% Ti for the Fe–20% Co–25% Cr alloy. A low titanium content insignificantly increases the oxygen concentration determined by the chromium content. At a higher titanium content (after the change of the mechanism of interaction of chromium and titanium with oxygen, when titanium determines the oxygen solubility in the melts), the oxygen concentration substantially decreases and, then, increases after passing a minimum point at a titanium content of ~0.9%. The minimum oxygen concentrations of these alloys are 1.8 × 10^–3 and 3.9 × 10^–3%, respectively.

The results of overloading and underloading tests of aluminum specimens in near-threshold crack growth rate range are considered. A combined model is proposed to take into account crack closure and the influence of the local stresses at the crack mouth. The model is based on the Neuber and Ramberg–Osgood equations and can be used to estimate the fatigue life of crack growth in the near-threshold range. This model is grounded from a physical standpoint.

The mechanical properties and the structure of the 08Kh18N10T steel/grade 10 steel bimetallic welded joint formed by explosion welding after step-by-step rolling at a reduction of ~10% per pass are studied. There is a zone of increased microhardness ~0.4 mm wide in the bimetallic weld region. An increase in the number of rolling passes decreases the width of this zone and the wave relief of the weld. First rolling passes result in nonuniform deformation of the bimetallic layers. Grade 10 steel, whose deformation resistance is lower in the initial state than that of the 08Kh18N10T steel, experiences the greatest deformation. Both bimetal layers deform uniformly during strain hardening the grade 10 steel. The mechanical properties of the bimetal, grade 10 steel, and 08Kh18N10T steel after the same plastic deformation are compared. The bimetal in the initial state has greater strength than its individual components. However, the 08Kh18N10T steel is hardened during rolling more intensely than the bimetal due to the formation of strain-induced martensite; therefore, the strength of the 08Kh18N10T steel significantly exceeds the strength of the bimetal as a whole at a total reduction of ~20% or higher. The initial stage of fracture along the bimetallic weld during rolling is shown to be associated with shear of the layers due to more intense spreading of the grade 10 steel layer. The curvature of the side surface of the bimetal strip increases as the strain increases, which generates tensile stresses in the direction of the strip height. This fact and the rolling-induced tensile longitudinal stresses result in a network of cracks in the bimetal layers along the maximum shears.