Journal of Superhard Materials最新文献

The application of metal coating on cubic boron nitride (cBN) particles surfaces has emerged as an effective strategy for enhancing abrasive bonding performance, with thermal stability of these coatings recognized as a critical parameter in practical applications. This study investigates titanium–copper (Ti–Cu) coatings deposited onto cBN particle surfaces through vacuum vapor deposition techniques. Experimental findings demonstrate that Ti–Cu coatings exhibit significantly enhanced thermal stability at elevated temperatures (750°C) compared to conventional titanium coatings. This advancement stems from the synergistic integration of precise vacuum deposition process control with the inherent advantages of Ti–Cu composite materials, offering promising solutions for next-generation abrasive tools such as grinding wheels and cutting instruments.

Some thermodynamic aspects of interaction between Ni–Fe–Co–Cr–Ti–Al high-entropy alloys (HEAs) and cubic boron nitride (cBN) at high temperatures in a medium with and without oxygen are studied. CALPHAD modeling with literature data are used to estimate the temperature dependence of change in the Gibbs energy for the formation of nitrides, borides, and oxides. It is shown that the presence of oxygen essentially changes thermodynamic conditions for the reactions, in particularly, decreases the probability of direct interaction between Ti, Al, and cBN due to the formation of oxide phases. Comparative analysis with reactions of pure metals indicates that Ti and Al in the composition of HEAs have a low activity to agree with CALPHAD calculation results. Experimental high-temperature studied performed by using the method of synchronous thermal analysis fully confirm thermodynamic calculations. The obtained results can be used to develop the compositions of high-entropy alloys for application in cBN based composite materials.

We developed an efficient computational model of thermal processes during friction stir welding (FSW) of heat-resistant alloys using a superhard tool. The model includes only the functional element and the welded components (plates), with appropriate boundary conditions applied to their surfaces. We selected these conditions based on computational experiments using a full model, which comprised the functional element, its tooling, the welded components, and a support plate. The choice of boundary conditions for the efficient model is justified by the contact surfaces of its elements with other FSW equipment and by the distribution of heat flux on the welded components directed toward the support plate. Neglecting heat flux distribution in simplified models introduces significant errors in calculating the temperature field within the welded components. Using the efficient model shortens computational time by a factor of 2 to 2.5 compared with the full model. Numerical experiments identify the FSW process parameters that ensure the thermal stability of the cyborite tool during welding, creating a reliable basis for process optimization.

Novel high symmetrical body centered carbon allotropes: cubic C₄₈ and tetragonal C₃₂ are proposed with respective original “ana” and “ukc” topologies. Devised from crystal structure engineering, their ground state structures and energy derived physical properties were accurately derived from quantum mechanics calculations within the density functional theory DFT. Both allotropes made of distorted tetrahedral C4 arrangements were found dense with ρ > 3 g/cm³ that remains lower than diamond density: ρ = 3.55 g/cm³. With cohesive albeit metastable ground state structures versus diamond, both allotropes show stability from the mechanical (elastic properties), dynamic (phonons band structures), as well as thermodynamic properties that show relationship with diamond’s experimental C_V = f(T) discrete results. Vickers hardness magnitudes H_V(C₄₈) = 47 GPa and H_V(C₃₂) = 59 GPa indicate super-hard materials. The electronic band structures range from large direct band gap ∼5 eV for C₄₈ to indirect band gap ~2.5 eV of semi-conducting-like C₃₂. Such findings of original allotropes with targeted physical properties are bound to enrich the field of research on carbon allotropes especially highly symmetrical ones.

The effect of the content of SiC additives to HfB₂ and their physicochemical properties (grain morphology and size of SiC powders, content and composition of their impurities, 6H or β crystal structure) on the level of compaction in hot-pressed ultra-high-temperature HfB₂–SiC composites, their mechanical properties (hardness, fracture toughness, Young modulus), and heat resistance (resistance to ablation) under heating in air to high temperature with a gas burner was studied. The Vickers microhardness H_V and fracture toughness K_Ic of the best from the developed composites were, respectively, H_V = 38.6 ± 2.5 GPa and K_Ic = 7.7 ± 0.9 MPa m^0.5 (after the indentor load of 9.8 N), and the Young modulus is 510 GPa. This composite was synthesized from a HfB₂–30 wt % SiC (5–10 µm) mixture under hot pressing (at a pressure of 30 MPa, 1950°C, 30 min) and had a density of 6.54 g/cm³. The studies of resistance to ablation in air for hot-pressed HfB₂ and HfB₂–SiC specimens heated with a gas burner show that HfB₂ ceramic with addition of 30 wt % SiC and an average grain size of 30–50 µm (clastic grains with sharp edges and an approximate stoichiometry SiC_1.6O_0.1, 6_H SiC) and 5–10 µm (single-crystal grains with a hypercubic nearly spherical shape almost free from impurities with an approximate stoichiometry SiC_1,5, β-SiC) are highly refractory: they are resistant to the temperatures of 2766 and 2780°C, respectively, at a mass loss of 0.25 mg/s as compared to the HfB₂ ceramic free from additives, the specimens from which were cracked as soon as at a temperature of 1870°C, and also more resistant than the HfB₂–30 wt % SiC ceramic synthesized with addition of SiC with sharp clastic grains with a size of 1 µm (with a shape lamellar or strongly elongated in one direction and an approximate stoichiometry SiC_4.6O_0.75, 6H-SiC) or 3–10 µm (with an approximate stoichiometry SiC_2.3O_0.25, 6H-SiC), which was cracked as soon as at a temperature of 1787 and 1455°C, respectively. A better heat resistance (resistance to ablation) exhibited by the HfB₂–SiC ceramic with addition of certain SiC types can be explained by high hardness and Young modulus values, the formation of solid solutions on the basis of HfB₂ and SiC phases with a small quantity of impurity oxygen, and the distribution of the present phases over the volume of the composite.

This study reports the preparation of AlN–TiN ceramic composites with high TiN content, near the percolation threshold, by pressureless sintering and examines their properties. The analysis addresses microstructural characteristics, measured thermal conductivity at room temperature, and electrical resistivity in the 300–700 K temperature range. The study also proposes a mechanism responsible for the drastic change in electrical conductivity in the as-obtained composites.

Using computational modeling, we optimized the resistive heating process of the high-pressure apparatus (HPA) cell designed for the growth of GaN crystals from the Fe–Ga–N solution-melt under high-pressure and high-temperature (HPHT) conditions via the temperature gradient method. The thermal state of the apparatus was simulated by solving the coupled electro- and heat-conduction problem using the finite element method. Modeling determined the spatial distribution of temperature and temperature gradient within the experimental cell. As a result of computational optimization of the thermal state of the toroid-40 type HPA cell, polycrystalline GaN was synthesized from the Fe–Ga–N solution-melt. Reducing the axial temperature gradient in the crystallization volume from 13 to 1.5°C/mm produced the growth of petal-shaped GaN single crystals. Observed crystal growth rates varied from 40 to 250 µm/h.

For the diamond grinding of ceramic silicon nitride balls, the advantages and shortcomings of performing the process when the balls are based on a plane and in a V-shaped groove under circular feed both with and without oscillation are considered. The reasonability of grinding the balls in a groove under circular feed without oscillation in certain processing regimes to preserve the flat shape of a diamond wheel or eliminate its concavity is shown. It is proposed to increase the efficiency of the diamond grinding of ceramic balls by passing to the process, in which the scheme of basing the balls is varied along with the features of their circular feed with the application of corresponding machining regimes.

This study examines the regularities in polishing optical components made of copper and aluminum using dispersed systems of micro- and nanopowders. The results show that both the material removal rate and the wear intensity of the polishing powder increase with higher Q factors of the microresonator, as well as with longer lifetimes of quantum dots on the polished surface and clusters on the surface of polishing powder particles in the excited state. The volumetric wear coefficients and the most probable sizes of sludge and polishing-powder wear nanoparticles exhibit corresponding trends. The surface roughness parameters R_a, R_q, and R_max increase linearly with the Q factor of the microresonator. Analysis of the dependence of the surface roughness parameter R_z and the η_m/R_a ratio on the most probable size of sludge nanoparticles indicates that using cerium dioxide powder dispersions for copper polishing fails to meet the required standards for optical surfaces, and for aluminum polishing, it does not offer sufficient material removal efficiency. The study substantiates the feasibility of employing copper metaborate micro- and nanopowder dispersions to polish optical copper and aluminum surfaces, achieving the required surface roughness at a high material removal rate. Theoretical values of the material removal rate during polishing with copper metaborate and cerium dioxide dispersions agree well with experimental data, showing a deviation of only 2–5%.

This study examines the interaction between titanium carbide TiC and nitride vanadium VN during both high-pressure, high-temperature (HPHT) sintering and mechanical alloying in a high-energy planetary mill. An equimolar TiC–VN mixture served as a binder in the synthesis of a PcBN composite with the cBN–TiC–VN–Al system (60 : 17.5 : 17.5 : 5 vol %) and was also used during mechanical alloying. Both synthesis routes produced confined solid solutions, (Ti, V)(C, N) and (V, Ti)N, but through distinct mechanisms: vacancy formation during mechanical alloying and diffusion-driven processes during HPHT sintering. Considering these findings, we propose synthesizing PcBN composites with various Me^IC–Me^IIN binders by applying preliminary mechanochemical treatment until solid solutions form.