L. I. Aleksandrova

Novel hybrid ultrahard material

A novel hybrid ultrahard polycrystalline composite material has been produced by the reinforcement of the polycrystalline diamond composite thermostable material with a CVD grown polycrystalline diamond. It has been found that a thermal treatment of a polycrystalline diamond grown at high pressure ensures an increase of the CVD diamond hardness from 77 to 140 GPa. Tests of drilling tools have shown that in turning granite of the XI drillability index the wear intensity of rock destruction elements of the hybrid ultrahard material is lower than that of rock destruction elements of polycrystalline diamond composite thermostable material by a factor of 14.

The diamond-tungsten carbide polycrystalline composite material

The sintering of a diamond composite from diamond and tungsten powders of submicron and nanosizes at high pressure and temperature has been discussed. It has been shown that as a result of the diamond and tungsten interaction tungsten carbide particles, which are chemically bonded to diamond particles, form in spaces between them. Over the whole volume of the composite the structure has been observed, where tungsten carbide and diamond grains are regularly placed and are uniform in size. An addition of a coarse diamond component to the composite has been found to contribute to an increase of the composite wear resistance. The optimal sintering parameters and formulation of this composite have been defined.

Structure, mechanical and functional properties of aluminum nitride-silicon carbide ceramic material

Two-phase ceramic composites of the dielectric-semiconductor type having different semiconducting phase content (aluminum nitride ceramics with uniformly distributed inclusions of silicon carbide of a certain size) have been produced by pressureless sintering. These composites are characterized by Vickers hardness HV (150 N) 9.5–15.8 GPa, Palmqvist fracture toughness 3.0–4.2 MPa m0.5, bending strength 132–209 MPa, thermal conductivity 37–82 W/(m K), and by a coefficient of the microwave electromagnetic energy attenuation to 36.3 dB/cm. It has been found that as the size of silicon carbide grains in aluminum nitride-based ceramics increases, the thermal conductivity increases and microwave energy attenuation decreases, which is indicative of the decisive role of grain boundaries in scattering both phonons and microwave radiation.

Structure and physico-mechanical properties of CVD diamonds of various crystalline perfections in the hybridite material

A comparison study has been conducted of the substructure of samples of CVD diamonds of various crystalline perfections in the hybridite material produced at high pressures and temperatures. The material thermostability and hardness variation as a result of the formation of a polycrystalline shell of diamond thermostable composite material around a CVD diamond at high pressure and temperature have been examined. Based on the data obtained on the efficiency of tools from hybridite with CVD diamonds of various structural perfections, the most efficient applications of tools have been recommended.

Structure and hardness of octahedral natural diamond single crystals depending on the HPHT treatment conditions

The structure evolution of octahedral natural diamond single crystals has been studied depending on the HPHT treatment using Raman scattering and infrared spectroscopy. It has been found that the formation of a polycrystalline diamond capsule around a single crystal at p = 8 GPa and T = 1500°C gives rise to a combined structural-stressed state in the single crystal due to its plastic strain. This state has been manifested by a significantly (more than double) broadening of the characteristic line of diamond (1332 cm−1) in the Raman spectrum and the increase of a single crystal hardness from 105 to 120 GPa.

The Effect of the Indentation Load on the Results of Measuring Hardness of Superhard Materials

The value of an indentation load on the Vickers indenter in measuring hardness of composite superhard materials has been substantiated. It has been shown that in hardness testing a 5N-load provides optimal chances for precise measuring the indent without damages around it.

Strength of diamond powders synthesized in the Mg-Zn-B-C system

The strength of diamond powders of grit size 125/100 μm synthesized in the Mg-Zn-B-C system (reaction mixtures having different boron concentrations) has been investigated. It has been shown that the distribution of strength by fracture load is correctly described by the Weibull function. The strength index of diamond powders and confidence intervals has been defined. It has been found that the strength index dependence on boron concentration in the range from 1 to 40 at % is described by the function having the minimum at 20%.

Diamond polycrystalline composite material and its properties

The results of experimental studies on the development of a diamond polycrystalline material to equip drill bits have been considered. Angles of wetting graphite by sintering aids Ni, Co, and alloy of them have been defined. Among the composites, which have been tested, the longest durability and the highest strength have been exhibited by the composite of the Cd-Co-34Ni formulation.

Comparative physico-mechanical characteristics of micron powders of synthetic and natural diamonds and polycrystalline composite materials based on them

Physico-mechanical characteristics of micron powders of synthetic (SD 40/28) and natural (ND 40/28) diamonds and of polycrystalline composite materials based on them have been studied. Both the powders have been shown to meet the requirements of DSTU 3292-95 (State Standard of Ukraine). At the same time the abrasiveness of natural diamond is higher than that of synthetic diamond, while the grain density and specific surface is lower than that of synthetic diamond grains. The elastic characteristics of sintered polycrystalline composite materials (the Young modulus, shear modulus, bulk modulus, Poisson ratio, and wear resistance in stone working by friction) of a composite sintered from the natural diamond micron powder are higher, while the life at cyclic compression is somewhat lower as compared to a composite sintered from the synthetic diamond micron powder.

Diamond polycrystalline composite material with dispersion-hardened nickel-based additive

A diamond polycrystalline composite material with improved physico-mechanical characteristics has been obtained at high pressure and temperature using nickel and cobalt powders and tungsten carbide nanopowder as sintering aids. Samples of this material reinforced with CVD polycrystalline diamond at high pressure and temperature have been manufactured.