Journal of Superhard Materials最新文献

Now there is still no unified standard for the evaluation of mixing uniformity in the abrasives industry. Taking the powders commonly used in resin bonded grinding wheels as the research objects, a simple sampling specification and uniformity statistical method were designed in this paper. By means of various detection methods, the homogeneity of the mixture was evaluated from macroscopic and microscopic perspectives. The results showed that organic solvent method was suitable for macroscopic analysis of resin bond. X-ray fluorescence spectrometry (XRF) was suitable for macroscopic analysis of fillers. Calcination method was suitable for macroscopic analysis of substances which can be oxidized in the air. The optical microscopy method was suitable for on-line real-time control of the raw material powders. Scanning electron microscope (SEM) observation was suitable for micro-uniformity analysis.

This study examines the electrical resistance of pressureless sintered ceramic composites of AlN–50 wt % SiC, which are suitable for use as bulk microwave radiation absorbers. For four groups of samples with quality factors Q = 30, 33, 37, and 44, the average surface resistances are 42, 64, 92, and 136 kΩ, respectively, while the average bulk resistances are 2.8, 4.1, 5.2, and 7.0 kΩ, respectively. An analysis of the experimental data revealed a correlation between surface and bulk electrical resistance. In general, higher bulk resistance corresponds to higher surface resistance. Moreover, as the quality factor increases from 30 to 44, the surface resistance exceeds the bulk resistance by factors ranging from 14.7 to 19.5.

For the diamond grinding of ceramic silicon nitride balls based on a plane with circular feed under oscillation, some results of experimental study on the effect of their positioning scheme and processing regime on the precision of their shape and the shape of the worn surface of a diamond wheel were reported. The shape accuracy criteria of ground balls were their diameter variation and the shape factor of their out-of-roundness profile and the radial slope angle of the working surface of a wheel and the curvature coefficient of its worn surface. This effect was described by adequate linear functions for the ball diameter variation from the wheel feed depth and rotation speed and the wheel profile inclination angle and curvature coefficient from the wheel feed depth and the rotation speed of the table with the balls. The processing regime parameters, at which the studied scheme of positioning the balls is reasonable, were predicted.

The study examined for the first time the effects of high (400 MPa) hydrostatic pressure (HHP) treatment on the phase composition and wear resistance of WC–15 wt % Co cemented carbide, as well as on the performance of tools equipped with this material during the smoothing of steel. The results demonstrated that HHP treatment induced a martensitic fcc → hcp transformation in cobalt, which enhanced the alloy’s strength. The impact of HHP treatment on the wear resistance of WC–15 wt % Co cemented carbide tools was investigated during the smoothing process of structural carbon steel 45. The treatment increased the tool’s wear resistance by 31%, compared to tools equipped with untreated cemented carbide. This improvement resulted from changes in the wear mechanism. While the wear of tools with untreated cemented carbide involved the detachment of massive clusters of WC and Co grains, the wear of tools with HHP-treated carbide was characterized by the removal of individual WC grains. One contributing factor to the observed effects is the compressibility of cobalt, which is twice that of tungsten carbide.

For the (26Fe–25Cr–32Cu–9Ni–8Sn) + ZrO₂ matrix material used in С_diamond–(Fe–Cr–Cu–Ni–Sn) composite materials formed by spark plasma sintering, the dependences of the relative density ρ_rel, ultimate compression R_cm and bending R_bm strength, microhardness H_V, and fracture toughness K_Iс on the zirconia content has been established by using samples with different ZrO₂ content. The addition of 10% ZrO₂ to the 26Fe–25Cr–32Cu–9Ni–8Sn composite increases the relative density ρ_rel from 0.987 to 0.997, the ultimate compression strength R_cm from 950 ± 35 to 1510 ± 45 MPa, the ultimate bending strength R_bm from 750 ± 20 to 1140 ± 35 MPa, the microhardness H_V from 8.0 ± 0.25 to 9.0 ± 0.42 GPa, and the fracture toughness K_Iс from 6.5 ± 0.35 to 9.2 ± 0.42 MPa m^0.5. Such parameters are caused by tetragonal t-ZrO₂ phase transformation and, correspondingly, an increasing role of transformation strengthening, and a decrease in the grain size, as ZrO₂ is an inhibitor of grains for the major Fe and Cr phases under sintering. In the 26Fe–25Cr–32Cu–9Ni–8Sn sample (({{C}_{{{text{Zr}}{{{text{O}}}_{{text{2}}}}}}}) = 0%) under indentation, there occur many cracks of considerable size both in the inner area of a Vickers pyramid imprint and around it to result in excessive brittleness and destruction in the material. This is due to agglomeration in the process of mixing the components, their separation under sintering, and the formation of micropores and microcracks to be a main reason of low values for ρ_rel, R_cm, R_bm, H_V, and K_Iс. At a zirconia nanopowder content ({{C}_{{{text{Zr}}{{{text{O}}}_{{text{2}}}}}}}) = 10%, the cracks in the matrix near the indentor imprint become poorly visible, and the material is not almost destructed in the vicinity of the indentor imprint. The results obtained for the relative density ρ_rel in combination with high mechanical characteristics (R_cm, R_bm, H_V, and K_Iс) of sintered (26Fe–25Cr–32Cu–9Ni–8Sn) + ZrO₂ matrix material samples enable their application for the production of composite diamond-containing materials with increased mechanical and service characteristics.

A novel carbon allotrope, hexagonal C₈, is proposed from crystal chemistry and quantum density functional theory (DFT) investigations of the ground state structures and pertaining physical properties. The structure possessing an unknown topology with 3,4²-c net exhibits corner sharing tetrahedra connected by cyclopropane-like C₃. C₈ was subsequently used as a template to devise original binary subnitride C₆N₂. Both the allotrope and the binary phase were found cohesive and stable mechanically (elastic constants and their combinations) and dynamically (phonons band structures) whilst presenting large hardness: H_V(C₈) = 60 GPa, and H_V(C₆N₂) = 49 GPa. The electronic band structure reveals conductive behavior for the allotrope and insulating one for C₆N₂ with E_gap ∼ 3 eV.

This study presents the results of research on the roughness height parameters and lateral forces on the faces of cubes and octahedra of diamond single crystals and constructs maps of their distribution. The research was conducted using atomic force microscopy (AFM) and lateral force microscopy (LFM) using samples of type Ib and IIa diamond single crystals, grown using the high temperature and high pressure (HTHP) method. It was found that for type Ib diamond single crystals, the surface roughness (Ra parameter) of the cube faces is 3.3 times smaller, and that of the octahedron faces is 1.5 times smaller than for type IIa diamond single crystals. Additionally, for type Ib diamond single crystals, the lateral forces on the cube faces are, on average, 3.5 times smaller, while those on the octahedron faces are, on average, 9.5 times larger than for type IIa diamond single crystals. The results suggest that the level of lateral forces on the faces of diamond single crystals is determined by the roughness of their surfaces.

Some characteristics are reported for modified hard alloy T5K10 formed under the conditions of purposeful control over the thermokinetic free vacuum sintering parameters minimizing the processes of solid- and liquid-phase interaction between tungsten carbide and cobalt, which determine the redistribution and recrystallization of carbide grains. The synthesized WС–(Ті,W)C–10Со hard alloy is characterized by a homogeneous finely grained structure, a high density (ρ = 12.98 g/cm³), a low level of residual microporosity, a bimodal composition of WC grains, and bridges between carbide grains. As compared to the commercial analogue, the synthesized hard alloy has a 2.4 GPa higher hardness (Н_V = 15), a 270 MPa higher mechanical bending strength, a 1.4 MPa m^0.5 higher fracture toughness, and 1.5 times higher wear resistance. The modification of sintering technology and structural transformations in the synthesized WС–(Ті,W)C–10Со hard alloy have result in a 2.5-fold increase in its service durability during rough steel turning (forged axles of a railway wagons platform) and, in the case of deep soil chiseling, an increase in abrasion resistance is 48%.

The possibility to create materials for use as a matrix of sintered composite diamond-containing materials (CDMs) is shown. The results of experimental studies on the dependence of the structure of 26Fe–25Cr–32Cu–9Ni–8Sn CDM matrices manufactured by spark plasma sintering on the ZrO₂ additive content (ranged from 0 to 10%) are presented. The development of metal matric composites based on Fe–Cr–Cu–Ni–Sn matrices with ZrO₂ additives is a new approach to replacing the basic materials, which are commonly used in tools for stone processing industry. In the initial state, a 26Fe–25Cr–32Cu–9Ni–8Sn composite sample has a nonuniform distribution of elements. It is shown that the addition of ZrO₂ micropowder to the 26Fe–25Cr–32Cu–9Ni–8Sn composite makes it possible to form a structure, whose parameters can be purposefully controlled by changing its concentration. Under such conditions, the composites containing the ZrO₂ additive have a more uniform distribution of elements. Stable correlations have been established between the ZrO₂ additive content and the microstructure parameters.

A quantitative analysis of the correlation between the technological properties of cubic boron nitride (cubonite) grinding powders, modified with a combined coating, and the performance characteristics of grinding wheels made with such powders has been conducted. The values of the paired correlation coefficients were obtained between the relative loss of abrasive and the surface roughness (parameter Ra) of the treated surface (dependent factors), the technological parameters of the coating, the processing efficiency, and certain morphometric characteristics and technological properties of the modified grinding powders (independent factors). Factors exerting the greatest effect on the relative consumption of cubonite grinding powder in wheels during grinding are the processing efficiency (correlation coefficient of 0.884) and certain morphometric characteristics, such as the roughness of the grain projection (correlation coefficient of 0.28 and 0.294). In the case of surface roughness (parameter Ra), the most significant factors are also the processing efficiency, with a correlation coefficient of 0.856, and the specific perimeter of the grain projection, with a correlation coefficient of 0.12. Recommendations for applying these results are presented.