Inorganic Materials: Applied Research最新文献

Abstract—The effect of thermal treatment on the microstructure, phase composition, and microhardness of Ni + B₄C composite coatings is studied. The coatings are deposited onto the surface of an austenitic steel by cold gas-dynamic spraying. The initial coating is shown to be a nickel matrix containing distributed B₄C particles. Thermal treatment causes diffusion processes in the coating, which results in the formation of Ni₃B and Ni₂B compounds. The average microhardness of the initial coating is 3.4 GPa, and heat treatment results in an increase in the coating microhardness due to the formation of hard nickel borides.

Abstract—The paper presents the results of a study of selective laser melted samples of 1CP ferromagnetic alloy powder and a mixture of 1CP and copper powders using the same set of process parameters. Optical microscopy, X-ray diffraction analysis, and differential scanning calorimetry provided the data on the macrostructure, phase composition, and degree of amorphization of the samples. The results of the study can be used for further research and development of technology for manufacture of soft magnetic composites via selective laser melting.

Abstract

The results of the stepwise-dilatometry study of the influence of the graphite content on the temperature dependence of the specific volume of nanocomposites based on high-density polyethylene and graphite are presented. It has been found that, for nanocomposites with the graphite content of 1.0–10 wt %, the first-order phase transition occurs at 115°C. For samples containing 15–20 wt % graphite, this transition occurs at 110°C. On the basis of the dilatometric curves, the glass transition temperatures of the nanocomposites have been determined. The kinetics and mechanism of crystallization of nanocomposites have been considered.

Abstract—The antifriction properties of fabric carbon-carbon composites paired with silicon carbide ceramics were studied under dry friction conditions. The influence of the reinforcing fabric orientation, it’s composition and heat treatment on the friction coefficient and wear rate of the composite was studied. The features of composite friction and wear mechanisms were studied for different contact configurations and different material properties. The features of friction and wear mechanisms of the composite were revealed for various contact configurations and material properties; the characteristic mechanisms of frictional surface destruction were found for individual structural elements (individual fibers, threads, layers of reinforcing fabric). The optimum reinforcement parameters for the antifriction properties of the composite were determined.

Abstract—The possibility of using finely dispersed additives made of local mineral raw materials for the manufacture of concrete based on sulfur binder has been established. At the same time, additives with a high specific surface area contribute to the formation of uniform small sulfur crystals on the surface of fine fillers, which makes it possible to improve the strength properties of sulfur concrete.

Abstract—The effect of mechanical and tribological properties of Al₂O₃ nanocomposite ceramics depending on the graphene content is studied. The samples are obtained using plasma-spark sintering in the solid state at a temperature of 1550°C. The friction of sintered samples without graphene and with a graphene content of 2 wt % is carried out according to the ball–disk scheme at room temperature without lubrication. It is shown that graphene reduces the coefficient of friction and wear. The dependence of microhardness on graphene content is constructed. The sample with a graphene content of 1% has the highest microhardness.

Abstract

The results are given for impact of defects in the deposited layer on the durability of melted samples made of 08Kh14N5M2DL steel grade operating under conditions of friction at heating temperatures up to 800–900°C and under significant loads in the tribological contact zone. Defects in the deposited layer are represented by pores, the lack of fusion, and fractures. The defects inside samples undergoing friction tests are determined using X-ray computer tomography. It is found that the wear resistance of the surfacing layer without defects decreases both with growing test temperature and with increasing load applied to tribological contact. The presence of a microfracture pattern inside the deposited layer is crucial to dramatically decrease wear resistance. The presence of porosity in the deposited layer affects the wear to a lesser extent.

Abstract—The microstructure, phase composition, and oxidation resistance of as-cast high-entropy alloys (HEAs) Al_0.25CoCrFeNi and Al_0.25CoCrFeNiCuAg_x (x = 0, 0.1, 0.2) have been studied. Oxidation was carried out at 700°C for 50 h in air. During the experiment, curves for the dependence of the specific weight gain on the exposure time were plotted. It has been shown that the introduction of copper has a slight effect on the resistance of the base Al_0.25CoCrFeNi HEA to oxidation, while additional (to copper) alloying with silver worsens the resistance of the samples to high-temperature gas corrosion.

Abstract—The emergence of a thermionic field in a process mixture under thermal diffusion chromium plating has been established. It has been shown that some oxide compounds contained in a process mixture participate actively in the emission process. A cell for measuring emission currents and the temperature of their occurrence upon heating has been designed. The contribution of the electric emission field upon saturation of parts during thermochemical treatment has been determined in comparison with the contribution of the concentration field.

Abstract

The temperature and heating rate affecting the shrinkage kinetics are studied for cylindrical workpieces obtained from submicron and fine aluminum oxide powder. The studies involve the powder from three batches: (1) submicron (~0.15 µm) α-Al₂O₃ powder, (2) submicron (~0.2 µm) α-Al₂O₃ powder having an amorphous layer deposited on the particle surface, and (3) fine (~1 µm) α-Al₂O₃ powder. It is established that the powder particles in all batches has a monocrystalline structure. The powder workpieces are sintered using the electric pulse (spark) plasma sintering (SPS) technique. The shrinkage curves are analyzed using the Young–Cutler and the Coble models. The kinetics of sintering workpieces is shown to depend on diffusion developing between the powder particles. The sintering kinetics of workpieces made from submicron powder depends on intensity of the grain-boundary diffusion. In the sintering workpieces made of finely dispersed powder, the kinetics is additionally dependent on simultaneously developing volumetric and grain-boundary diffusion. It is established that the presence of an amorphous layer on the surface of particulate α-Al₂O₃ having submicron size affects the rate of migration of grain interfaces and the parameters of the Coble equation at the final SPS stage. It is assumed that the accelerated growth of grains and an increase in the microhardness of samples obtained through sintering workpieces made from submicron powder with an amorphous layer on the particle surface is caused by a higher density of defects at the grain interfaces. The elevated density of defects at grain interfaces can result from crystallization of the amorphous layer.