Journal of Superhard Materials最新文献

Two main varieties of cubic natural diamond crystals and the morphology of their faces have been characterized to demonstrate their distinction from cubic synthetic diamond crystals. The morphological features of cubic diamond crystals are caused by the mechanisms of their growth.

Low strength synthetic diamonds of the AS6–AS32 series used for diamond grinding processes are characterized by increased roughness and porosity, and the presence of impurities and inclusions. The article provides specific quantitative parameters of the above characteristics and shows how they affect the physical and mechanical properties of diamond. The possibilities of application of such defective synthetic diamonds of low strength are considered. It has been proven that their defectiveness can be a positive characteristic in the case of application in a grinding tool, since the presence of impurities and inclusions in diamonds together with their natural porosity can improve the strength index after additional heat treatment and increase the retention of grains in the binding material of the grinding wheel. Boundary conditions for the strength index of diamond grains are determined for the case when the presence of defects is a positive characteristic. The defect parameters of diamond grains in the event of changing their strength index are given and it is shown which type of defect can increase the performance of diamond wheels.

Using CBN, Si₃N₄, Al₂O₃, AlN and Y₂O₃ as raw materials, PCBN tool materials were prepared by high temperature and high pressure. The effects of sintering temperature (1400–1700°C) on the microstructure, mechanical properties and cutting performance of tool materials were studied. The results show that PCBN tool materials with higher density and better comprehensive properties can be obtained by using high temperature and high pressure technology. At 1500°C, it was observed that the α-Si₃N₄ in the binder had a tendency to transform to β-Si₃N₄, and the grains were well developed. With the increase of sintering temperature, the density, flexural strength, and hardness of the samples increased continuously. At 1700°C, the flexural strength and hardness reached 879.6 MPa and 38.8 GPa, respectively. At the same time, the cutting performance of the samples sintered at 1700°C is also the best. When cutting ductile cast iron with a cutting distance of 7 km, the tool wear is the smallest, which is 0.26 mm.

It is known that the theory of contact interaction of rough surfaces is based on roughness parameters and, first of all, on the reference profile curve (on which this study is focused) and how it is related to other roughness parameters. It is shown that the greater index tp of the relative length of the reference profile, the greater the bearing capacity of such a surface. That is, the higher the reference curve rises, the greater the tp parameter. For example, at the level of 20 or 50% Rmax, the greater the degree of filling of the rough surface, the greater its bearing capacity. The surface area located below the reference curve characterizes the degree of filling of the rough surface with the finishing material. It is shown that the plasma effect of medium power generally has a positive effect on the treated surface when the surface has not yet melted, which leads to a certain degree of ordering and substantial improvement of the supporting surface. Plasma exposure with melting worsens both the microroughness height and the bearing capacity of the surface. It is proved that the simultaneous use of compacts and diamond grains in wheels allows one to achieve a decrease in the roughness of the treated surface and to obtain the specific microroughness profile, in which a surface with the increased degree of microprofile filling and the increased bearing capacity is obtained, when so-called “lubricant pockets” are formed.

The structure and mechanical properties (hardness Н, elasticity modulus Е, estimative parameters for determining the resistance to elastic H/E and plastic Н³/Е² deformations, ultimate bending R_bm and compression R_cm strength) of diamond-containing С_diamond–WC–Co–CrB₂ composite materials (DCM) formed by spark plasma sintering and the ability of their hard-alloy matrix to retain diamond grains from falling out have been studied as a function of the chromium diboride content (within a range from 0 to 10 wt %). It has been established that the addition of CrB₂ at a concentration of 4 wt % to 25C_diamond–70.5WC–4.5C leads to an increase in the ultimate bending R_bm (from 2040 ± 20 to 2375 ± 50 MPa) and compression R_cm (from 5100 ± 30 to 5650 ± 70 MPa) strengths and in the estimative parameters for determining the resistance to elastic H/E (from 0.043 to 0.051) and plastic Н³/E² (from 0.062 ± 0.0040 to 0.080 ± 0.0070 GPa) deformations. A further increase in the CrB₂ concentration (to 10 wt %) in a specimen leads to a gradual decrease in the ultimate bending R_bm (to 1840 ± 80 MPa) and compression R_cm (to 5100 ± 100 MPa) strengths with a growth in Н/E (to 0.054) and Н³/Е² (to 0.088 GPa). As a criterion for estimating the hard-alloy matrix ability to retain diamond grains from falling out, it is proposed to use the state of the surface relief of fracture in a DCM specimen. Under such a condition, the relief surface of diamond is indicative of strong adhesion between diamond grains and a hard-alloy matrix. The destruction of a DCM specimen along the diamond–matrix interface indicates that the adhesion between diamond grains and a hard-alloy matrix is weak to worsens the performance characteristics of such DCMs. It has been shown that the mentioned mechanical and performance characteristics of DCM specimens can be attained by adding 4 wt % of CrB₂ into DCMs to decrease the growth rate of WC grains and, as a consequence, to form a homogeneous fine-grained microstructure in their hard-alloy matrix.

Some results of experimental studies on the specific features inherent in the intermittent cutting of quenched steel AISI 52100 with a PcBN tool were presented, and the process of machining with a PcBN tool was analyzed by using the finite element method with consideration for the polycrystalline structure and composition of the tool. To ascertain the effect of the PcBN composite composition on the cutting forces and tool wear, experiments were conducted with cutters of two types of materials with different PcBN content. The obtained experimental results demonstrated the efficiency of the PcBN tool with a low PcBN content to be comparable with the tool characterized by a high PcBN content in the machining of quenched steel AISI 52100 at a cutting speed of 210 m/min under intermittent cutting conditions. The obtained results indicated the prospects and high performability of tools manufactured from PcBN composites of different composition under certain operational conditions.

We present the results of the study of the microstructure of a ceramic composite based on aluminum nitride with different concentrations of yttrium oxide, synthesized by pressureless sintering. The thermal conductivity of the obtained materials was investigated, and the optimal amount of yttrium oxide in the composition for sintering large-sized parts used in electrotechnical devices was determined.

The wear of functional components of rock-crushing tools with composite diamond-containing materials (DCM) based on a metal binder sintered by resistive electrosintering under pressure in the process of grinding of sandstone from the Torez deposit is studied. A characteristic named the degree of reinforcing of the working surface of the DCM functional components is proposed, which is determined from the ratio of the total area of the diamond cutting grains to the area of the working surface of the functional component. The dependence of the intensity of wear of DCM functional components on the degree of diamond reinforcement of their working surfaces is plotted. During the tests, rock destruction products and wear (sludge) fragments of DCM functional components are collected and analyzed using digital image processing tools, as a result of which morphometric characteristics of the sludge as a function of the degree of reinforcement of the DCM component working surfaces with diamond grains are obtained. Using the colorimetry method, metal binder fragments of the DCM are isolated from the total mass of sludge and their size distribution is determined. The results of morphometric analyses of the wear products of the diamond-containing composite tool and the rock destruction products are given.

As a reinforcement phase to form metal matrix composites, graphene has attracted more and more attention due to its excellent properties i.e. optical, electrical and mechanical properties. However, the dispersion of graphene has always been an important factor that significantly effects its development. This paper mainly summarizes the physical methods to improve the dispersion of graphene and analyzes its internal mechanism, moreover the advantages and disadvantages of these methods are depicted and compared. Finally, the improvement of the dispersion of graphene and its future applications are prospected.

As a result of studying the laws of interaction of sludge particles and polishing powder wear particles during polishing of polystyrene, polymethyl methacrylate, and polyallyldiglycocarbonate with use of dispersed micro- and nanopowder systems, it is found that the total number of sludge nanoparticles and wear powder nanoparticles of tools exceeds the number of polishing powder particles and the total volume of the former is much smaller than the volume of the contact zone. It is shown that the scattering of sludge particles on the wear particles of the polishing powder occurs at angles of 90° to 160°. The effective differential cross section of nanoparticle scattering is in the range of 0.3–4.4 Tb. The maximum value of the scattering angle and the minimum value of the effective differential scattering cross section, which are observed when polishing polystyrene using a dispersed system based on cerium dioxide, indicate the highest probability of plaque formation from nanoparticles of wear polishing powder on the treated surface.