Inorganic Materials: Applied Research最新文献

Abstract

The changes in the phase composition and porosity of plasma-sprayed Al₂O₃ ceramic before and after its treatment by hot isostatic pressing (HIP) have been studied. The treatment was performed using a HIP facility with a graphite resistance heater in an argon atmosphere at a temperature of 1600°C at a gas static pressure of 200 MPa for 3 h. The phase composition of the material was determined using quantitative phase analysis. The porosity of the ceramic was determined by X-ray computed tomography. It has been established that, just at the end of plasma spraying, the ceramic material contains a set of α-, γ-, and δ-modifications of Al₂O₃, which differ in the density and type of crystal lattice. The total ceramics porosity was 18.9 vol %. After treatment using HIP, the metastable γ- and δ-Al₂O₃ phase modifications disappeared, and the stable α-Al₂O₃ modification occupied the entire volume of the ceramic material. The total ceramics porosity decreased to 9.7 vol %.

Abstract—This paper presents the effect of hot gas extrusion (HGE) parameters on the phase composition and mechanical properties of composite rods composed of a core with reaction products of a Ni–Al powder mixture and a steel shell at room temperature. Composite rods are produced in three HGE modes depending on the initial extrusion temperature and the gas pressure in the chamber with parent materials. The phase composition of the produced materials is studied. It is found that the extent of the reaction of the powder mixture increases at higher temperatures of the initial HGE and, accordingly, low gas pressures, but unreacted nickel and aluminum particles remain at the lowest temperature of the initial HGE (at a higher gas pressure). Three-point bending tests show that the yield strength of the composite rod whose core contains plastic inclusions of the parent nickel and aluminum is higher than the yield strength of the steel rod. The rods with the maximum extent of the reaction are observed to have the highest microhardness.

Abstract—The kinetic regularities of the process of structural modification of highly dispersed powders of a saponite-containing material after mechanical dispersion are studied. Changes in the specific surface of the powders at different grinding times and exothermic thermal effects (changes in enthalpy) in a temperature range of 810–820°C are used as information criteria characterizing the rearrangements of the crystal lattice of the minerals. It is determined that, in the case of mechanical grinding of a saponite-containing material for more than 20 min, its structural changes leading to the formation of serpentine occur intensely. It is found that, in this case, the traditionally used criterion for evaluating the process of mechanical grinding of raw materials by the specific surface of the powder is not a sufficient information parameter when optimizing the structural changes in experimental specimens. The predominant parameter of this process is the enthalpy factor that characterizes the thermal effect of the structural modification.

Abstract

Contemporary research methods are used to study in detail the structure and phase composition of the (Sm, Zr)(Co, Cu, Fe)_z alloys with z = 5.5–7.0 in the as-cast state and after heat treatment, which includes the solid-solution treatment at 1150–1180°C for 5 h, subsequent water quenching, isothermal aging at 800°C for 20 h, and cooling (stepped aging) from 800 to 400°C at an average rate of 100°C/h. The transformation scheme of boundary structural constituent of a (Sm, Zr)(Co, Cu, Fe)_z permanent magnet manufactured by powder metallurgy technology is proposed for different heat treatment stages. The formation mechanism of the high-coercivity state of a permanent magnet in the course of complete cycle of heat treatments is given in the form of a sequence of phase transformations accompanied by the redistribution of a number of constituents of the (Sm, Zr)(Co, Cu, Fe)_z alloy.

Abstract—The work is aimed at improvement of the mechanical properties of polymers produced using laser stereolithography technology by modifying the composition of a photocuring resin (PCR) with a highly dispersed filler. A composition based on vinyl ester resin was developed as the starting material, and aluminum hydroxide was chosen as the filler. The addition of the filler to the original PCR leads to a noticeable increase in the viscosity of the composition at 25°C. Specimens obtained both by laser stereolithography technology and by initiating polymerization by incoherent UV radiation were studied simultaneously for comparison. A thermomechanical analysis of the specimens was carried out and their studies were carried out using the differential scanning calorimetry method to determine the thermomechanical characteristics and the degree of conversion of double bonds for these specimens. It has been confirmed that post-curing of specimens is a necessary step in achieving their high mechanical properties. It has been shown that the use of aluminum hydroxide as a PCR filler improves the physicomechanical and thermomechanical properties of cured specimens.

Abstract

The results of studies on the zirconium crystal structure after initial stages of oxidation in an open air at temperature of 700°C for 15 min are presented. Samples of commercial pure zirconium with a minimal content of impurity atoms as well as chromium-alloyed zirconium have been studied by means of the action of compression plasma flows. The possibility of alloying the zirconium near-surface layer with chromium, with a chromium coating thickness of 1 μm, by means of compression plasma flows with the absorbed energy density of 25–43 J/cm² has been demonstrated. Stabilization of the high-temperature zirconium β phase in the form of β-Zr(Cr) solid solution and intermediate martensite α'-Zr phase has been observed. After isothermal annealing of zirconium samples at T = 700°C and irradiated with plasma flow with Q_max = 43 J/cm², no effect of the surface layer alloying with chromium atoms has been observed owing to its intense evaporation and ablation in the course of surface heating by plasma flow, as well as increased resistance to high-temperature oxidation at the initial stages in comparison with the initial state.

Abstract

The surface of monocrystalline silicon irradiated with a high-power pulsed beam of carbon ions and protons is studied using optical and scanning electron microscopy. The surface is irradiated using a TEMP-2 accelerator in a vacuum of ~10^–3 Pa. The ion beam consists of 70% carbon ions (C⁺ + C⁺²) and 30% protons. The sample is irradiated with one pulse with a dose of 1.5 × 10¹³ ions/cm². Craters characterized by a hexagonal shape are obtained on the silicon surface. X-ray diffraction analysis shows the presence of carbon content inside the crater.

Abstract

The results of ablation experiments are given for the case for a scanning beam of nanosecond range pulsed laser radiation using targets made of high-carbon U13 and low-carbon St30 steel grades. The dependence of the depth and power efficiency of ablation on the power density is determined in the range q = 4 × 10⁸–10¹⁰ W/cm². It is established that the maximum efficiency of removing the material is obtained when q = 4 × 10⁹ W/cm² for a target made of U13 steel and q = 7 × 10⁸–5 × 10⁹W/cm² for St30 steel. The size distribution is estimated for emitted microparticles. It is established that irradiation of high-carbon steel results in generating a flow of particles deposited on the target surface (back flow). The mechanism of this back flow is associated with formation of nanosized condensate particles. On the basis of the reflectivity measurements and on the studies of the microstructure of the irradiated surface using electron microscopy methods, a hypothesis is put forward that the higher ablation efficiency of high-carbon steel U13 compared to low-carbon steel St30 depends on the process of condensation of supersaturated carbon vapor on the target surface. This process can increase the absorption capacity of the irradiated target surface. As a result, the efficiency of material removal during the subsequent scanning pass is increased.

Abstract—Comparative durability tests of carbide cutting tools with (Ti, Al)N–Cu and (Ti, Al)N–Ni coatings applied to its working surfaces were carried out under conditions of continuous and interrupted cutting of steels 09G2S and EP302-Sh, respectively. Under milling conditions of EP302-Sh steel, using VK6NST inserts with (Ti, Al)N–Cu and (Ti,Al)N–Ni coatings, the tool life increases by 3.1 and 1.7 times, respectively. When turning the 09G2S steel using VK6NST inserts coated with (Ti, Al)N–Cu and (Ti, Al)N–Ni, the tool life increases by 7.6 and 10.8 times, respectively, and the cutting forces F_z, F_x, and F_y are reduced by ~20%. It is shown that this effect is determined by the presence of a nanostructure in the formed coatings and the presence of a highly consistent ceramic component and ductile metal, which determine their hardness (more than 35 GPa) and fracture toughness (relative work of plastic deformation during indentation over ~60%) and increased tribological characteristics (friction coefficient of ~0.5 compared to uncoated carbide of ~0.7).

Abstract

The influence of the parameters of high-energy, thermal, and magnetic-pulse processing on the formation of the phase composition and magnetic properties of nanocrystalline powders of the Fe–O system during their production from cheap problematic iron ore raw materials “blue dust” of the Indian deposit has been studied. The results of research showed that the GR-1 concentrate “blue dust” in its properties refers to waste, and not to natural ore material. The presence of an oxide-salt layer on the surface of the particles and the high dispersion of the material do not allow it to be used in its pure form as a feedstock for blast-furnace production, and the development of a processing method requires a separate approach. From the analysis of the results of measuring the magnetic properties, it follows that, as a result of the processing of iron ore material in a high-energy planetary ball mill, it was possible to obtain samples with properties characteristic of hard magnetic materials. The particle size is 1 μm and the values of the coercive force and remanent magnetization are 190 Oe and 0.5 kG, respectively. This makes it possible to recommend the use of this magnetic material as fillers for polymer films. The conditions of thermal and magnetic treatment are determined, which make it possible to increase the values of the coercive force by 27–35% and the remanent magnetization by 1.9–2.6 times.