Vol 2017, No 7 (2017)

It is shown that powders of a model high alloy consisting of spherical particles 25–50 μm in size can be synthesized from a starting ultradispersed powder, which is made of a mixture of the alloy components and is fabricated by the magnesiothermal reduction of metal chlorides in the potassium chloride melt. The synthesis includes the stages of microgranulation of an ultradispersed powder, heat treatment of microgranules, classification of the microgranules with the separation of microgranule fraction of 25–50 μm, spheroidization of the separated fraction in a thermal plasma flow, and classification with the separation of a fraction of micro- and submicrometer-sized particles.

The heterophase interaction of Al₂O₃ refractory nanoparticles with a surfactant impurity (antimony) in the Fe–Sb (0.095 wt %)–O (0.008 wt %) system is studied. It is shown that the introduction of 0.06–0.18 wt % Al₂O₃ nanoparticles (25–83 nm) into a melt during isothermal holding for up to 1200 s leads to a decrease in the antimony content: the maximum degree of antimony removal is 26 rel %. The sessile drop method is used to investigate the surface tension and the density of Fe, Fe–Sb, and Fe–Sb–Al₂O₃ melts. The polytherms of the surface tension of these melts have a linear character, the removal of antimony from the Fe–Sb–Al₂O₃ melts depends on the time of melting in a vacuum induction furnace, and the experimental results obtained reveal the kinetic laws of the structure formation in the surface layers of the melts. The determined melt densities demonstrate that the introduction of antimony into the Fe–O melt causes an increase in its compression by 47 rel %. The structure of the Fe–Sb–O melt after the introduction of Al₂O₃ nanoparticles depends on the time of melting in a vacuum induction furnace.

Branch pipes (segments of fuel claddings of a full cross section) and ring specimens of two sizes were subjected to tensile tests. The experimental results are used to plot hardening curves, which are true stress–strain curves. The set of these curves is employed to plot the desired flow surface of EK-181 steel.

The study and application of the materials that are stable in the temperature range up to 1000°C are necessary to repair forming dies operating in this range. Nickel-based alloys can be used for this purpose. The structural state of a nickel alloy layer deposited onto a KhV4F tool steel and then heat treated is investigated. KhV4F tool steel (RF GOST) samples are subjected to laser deposition using a pulsed Nd:YAG laser. A nickel-based material (0.02C–73.8Ni–2.5Nb–19.5Cr–1.9Fe–2.8Mn) is employed for laser deposition. After laser deposition, the samples are subjected to heat treatment at 400°C for 5 h, 600°C for 1 h, 800°C for 1 h, and 1000°C for 1 h. The microstructure, the phase composition, and the microhardness of the deposited layer are studied. The structure of the initial deposited layer has relatively large grains (20–40 μm in size). The morphology is characterized by a cellular–dendritic structure in the transition zone. The following two structural constituents with a characteristic dendritic structure are revealed: a supersaturated nickel-based γ solid solution and a chromium-based bcc α solid solution. In the initial state and after heat treatment, the hardness of the deposited material (210–240 HV_0.1) is lower than the hardness of the base material (400–440 HV_0.1). Only after heat treatment at 600°C for 1 h, the hardness increases to 240–250 HV0.1. Structure heredity in the form of a dendritic morphology is observed at temperatures of 400, 600, and 800°C. The following sharp change in the structural state is detected upon heat treatment at 1000°C for 1 h: the dendritic morphology changes into a typical α + γ crystalline structure. The hardness of the base material decreases significantly to 160–180 HV_0.1. The low hardness of the deposited layer implies the use of the layer material in limited volume to repair the forming surfaces of dies and molds for die casting. However, the high ductility of the deposited layer of the nickel-based material is a prerequisite for a high stability under thermocycling loading conditions.

The influence of the technological parameters of selective laser melting (SLM) on the structure–phase state of a ZhS6K-VI nickel superalloy synthesized is studied by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. A nickel solid solution, an ordered γ' phase, and carbide inclusions form in the alloy at a scanning speed of 600–1200 mm/s, a laser beam power of 170–200 W, and various melting strategies. The following texture is shown to form in the alloy during SLM: the laser scanning plane predominantly coincides with the crystallographic {100} plane. The lower the scanning speed or the laser power, the stronger the texture. The alloy of found to be susceptible to cracking, which decreases with increasing scanning speed.

The physicochemical and the structural properties of the nickel-based melts with a low (impurity) bismuth content, which, like lead, is one the most harmful impurities in cast high-temperature nickel-based superalloys, are studied using the surface tension and the density. It is found that the surface tension increases as the bismuth impurity content varies from zero to 0.05 wt %, which corresponds to transition of excess substance from the surface into the volume.

It is shown that the literature data on the mechanism of the carbothermal reduction and sublimation of phosphorus from oxide melts are contradictory. The results of our studies are presented. An experimental procedure is proposed to calculate the reaction rate on the unit surface of the reducing agent. The regime and kinetic characteristics of the process change with the concentration of P₂O₅ in the oxide melt, the temperature, and the presence of impurities and metallic phase in the melt.