Journal of Superhard Materials最新文献

The results of studying the thermal conductivity of hot-pressed AlB₁₂–AlN ceramic composites with different AlN concentrations were presented. The thermal conductivity coefficient was measured for composite specimens at room temperature and approximated for AlB₁₂.

In the framework of a crystallochemical approach, new hexagonal (P6₃/mc) sp³-bonded BN polytypes (4H, 6H and 8H) and ternary BC₂N were proposed by rationalized substitutions of C for B and N in hexagonal carbon allotrope C₈ (4C carbon) with cfc topology, and density functional theory calculations of their ground states were performed. All new phases were found to be cohesive and stable mechanically (elastic constants) and dynamically (phonon band structures). According to modern models of hardness, the new phases were recognized as superhard with Vickers hardness above 50 GPa. Their electronic band structures exhibit insulating behavior with large band gaps.

Research on grinding high-speed steel with cubic boron nitride wheels has revealed challenges in evaluating the energy efficiency of grinding with diamond abrasive wheels made of superhard materials (SHMs) for hard-to-machine tool materials. These challenges arise due to the specific energy consumption index of the grinding process, which determines the ratio of effective grinding power. In addition to considering specific energy consumption and the energy efficiency coefficient of the process corresponding to the processing process, it is imperative to account for the wear of diamond abrasive wheels through the index of relative consumption of SHM grains in the working layer of the wheel during grinding. A novel relationship for calculating the energy efficiency coefficient (EEC) for diamond abrasive processing with SHM wheels has been proposed. It has been demonstrated that reducing the temperature in the grinding zone enhances the energy EEC. To achieve this temperature reduction, it is advisable to avoid metallic coating on the grains of SHMs and instead utilize an increased concentration of SHM grains in the working layer of the wheel. This adjustment results in an augmentation of the energy EEC, as elucidated by the proposed equation for calculating the EEC.

The results of experimental study on the effect of the treatment regime on the shape accuracy of balls and the surface wear of a diamond wheel are presented for the diamond grinding of silicon nitride ceramic balls in an annular groove and with circular feed. The indicators of the shape accuracy of ground balls are the variance of ball diameters, the out-of-roundness profile shape factor, and wheel surface wear characterized by the radial working surface tilt angle and curvature coefficient. This effect is adequately described by the linear dependences of the ball diameter variance on the circular feed rate and wheel speed, the shape factor on the wheel speed, and the tilt angle and curvature coefficient on the circular feed rate. The treatment regime parameters, at which the studied ball grinding scheme is reasonable for application, are predicted.

A TiC coating was rapidly formed on the surface of diamond particles by thermal explosion reaction using Ti/Carbon black/PTFE/Diamond powders as raw material. XRD and SEM were used to analyze and observe the phase composition and microstructure of the coating. Results show that the phase composition of bonders was TiC, Ti, and TiF₃ after thermal explosion reaction. The diamond surface obtained after the reaction can achieve good coating. Changing the diamond content in the raw material can regulate the phase composition of the coating. The coating on the diamond surface was mainly composed of TiC. When the diamond content in the raw materials was 20–40%, the coating was composed of TiC and TiF₃. When the diamond content in the raw material was 60–80%, the coating was composed of TiC and Ti.

We analyzed the results of the sessile drop method to examine experimental data regarding the behavior of liquid droplets on heterogeneous surfaces under the action of a magnetic field, their movement along the surface due to horizontal external forces, and in cases of detachment and dropping of the droplet onto a solid surface, compared to the outcomes of the simulation results obtained using the lattice Boltzmann method within a two-dimensional model. In most cases, there was a satisfactory qualitative agreement observed between the calculated and experimental data. This demonstrates the suitability and effectiveness of the proposed theoretical approach in exploring a broad spectrum of phenomena associated with the contact interaction between liquid and solid heterogeneous phases at both the meso- and macroscopic levels.

New data on the effect of a ZrO₂ nanopowder additive (from 0 to 10 wt %) on phase formation and structural transformations in the hard-alloy matrix in the region of destruction under impact loading and on diamond retention in composite diamond-containing 25С_diamond–70.5WC–4.5Co materials formed by spark plasma sintering are presented. The sintered initial 94WC–6Co composite consists of the hexagonal WC phase with unit cell parameters a = 0.2906 nm and с = 0.2837 nm, the cubic Co₃W₃C phase (а = 1.1112 nm), and the hexagonal graphite phase. The sintered composites with ZrO₂ content from 0.5 to 10% is composed by the WC and Co₃W₃C structural phases, amorphous carbon, and the tetragonal ZrO₂ phase (а = 0.36019 nm, с = 0.5174 nm). It has been shown that, when the ZrO₂ content is increased, the sizes of phase components and average microstrains are more rapidly decreased in directions с and а of the 94WC–6Co composite. The addition of ZrO₂ to the 25С_diamond–70.5WC–4.5Co composite improves diamond retention. In the sintered composites, diamond retention is improved due to that they have a higher content of the tetragonal ZrO₂ phase, which provides the transformational mechanism of strengthening in the hard-alloy matrix material via its structural transformations into a denser one and the formation of a more fine-grained matrix structure with thin interlayers of cobalt bonds between WC grains.

The investigation revealed patterns in the formation and localization of deposits of polishing powder wear nanoparticles on the processed surface during the polishing of polymeric materials using disperse systems of micro- and nanopowders. The total scattering cross section of polishing powder wear nanoparticles on sludge nanoparticles increases nonlinearly with the movement of particles, extremally depends on the product of spectral separation for dielectric constant separation between the processed material, polishing powder, and the disperse system, and exponentially increases with the resonator detuning. When polystyrene is polished using cerium dioxide micropowder, deposition on the processed surface is most likely to occur, with the maximum value of the total scattering cross section of polishing powder wear nanoparticles on sludge nanoparticles being at 49.7 Mb. Experimental data indicate that the localization of deposits with polishing powder wear nanoparticles on the processed surface occurs according to the distribution function of the total scattering cross section of polishing powder wear nanoparticles on sludge nanoparticles across circular zones, which aligns well with experimental results, within 12.5%. The experimentally determined average thickness of the deposit fragments of polishing powder wear nanoparticles, forming complete or partial coverage of the component surface, ranges from 1.1 to 1.5 µm.

The behavior of type IIa HTHP single crystal diamonds under shock loads created by means of Hopkinson–Kolsky pressure bars is studied. Controlled variation of load pulse magnitude and duration makes it possible to trace the complete history of crack progression. It ranges from crack initiation in regions of peak stress, through rapid crack propagation and the formation of a smooth surface, to stable crack growth accompanied by the formation of a densely packed array of fine ridges, and eventually to a deceleration and discontinuous crack movement, which culminate in a stepped structure upon the completion of step formation. Atomic force microscopy is employed to reveal the topographic characteristics of the fracture surface with spanning dimensions from 3 to 600 nm. The three-dimensional distribution of equivalent von Mises stresses throughout the entire crystal and respective crystal fragments after brittle fracture is also simulated in the study.

The influence of the rate of sintering by electron beam sintering (EBS) and spark plasma sintering (SPS) methods on the formation of the microstructure and properties of a 90 wt % WC + 10 wt % FeCrNiWMo composite is studied. The effect of technological parameters of sintering on structure formation and phase composition of a metal ceramic composite with high entropy bonding is determined. The change in the stoichiometric composition of tungsten carbide after sintering the composite by the SPS method is investigated. The mechanical properties (strength, hardness, crack resistance, and compressive strength) of the samples sintered by the EBS and SPS methods are compared. It is found that the electron beam method is more promising than the spark-plasma method when sintering a metal ceramic composite with high entropy bonding under optimal conditions. The study results can be used in toolmaking and in the military industry for manufacturing armor piercing cores of ammunition for small arms.