Influence of Shock Wave Treatment of Boron Carbide Powders on the Structure and Properties of Hot-Pressed Polycrystals Based on Such Powders

The influence of deformation pre-treatment (milling in a planetary mill and shock-wave treatment) of B₄C powders of different size composition on their structure as well as the structure and mechanical properties of samples that have been hot-pressed from these powders is investigated. It is shown that treatment by shock waves produces a substantial change in the structure of the powders, and this tends to increase the mechanical properties of the polycrystalline cakes. __________ Translated from Poroshkovaya Metallurgiya, Nos. 7–8(444), pp. 118–127, July–August, 2005.     

Structure of intermediate carbon phase formed under shock compression of ultradispersed graphite materials

We have studied the structure of the products of high-temperature shock compression of wood charcoal by x-ray diffractometry and transmission electron microscopy. We have shown that as a result of phase transformations at high pressures (30 GPa) and temperatures (above 2500 K), besides nanocrystalline diamond we see formation of an amorphous carbon phase having a density intermediate between the densities of the original charcoal and diamond. Based on comparison of the observed diffraction patterns with the patterns calculated for different models for amorphous carbon, and also considering the intermediate value of the density for the amorphous phase, we have concluded that this phase has the short-range order of the hypothetical H-6 structure, characterized by a three-dimensional framework of sp² bonds. The amorphism of the intermediate phase is due to both the crystallographic nature of the H-6 structure and the disorder of the original structures, the regular rearrangement of which to form crystalline structures is not possible. __________ Translated from Poroshkovaya Metallurgiya, Nos. 1–2(447), pp. 104–111, January–February, 2006.     

Structure of deformed polycrystalline zirconium carbide

Numerous studies have been conducted on the transition metal carbides for establishing the regularities of their plastic deformation [1, 2]. However, the relationship between the evolution of the deformation microstructure, the structural changes occurring at the micro-and the macrolevels, and the mechanical properties of the polycrystalline materials has not been investigated in sufficient detail. In view of this, we studied the dislocation structure of ZrC_x at different stages of deformation and over a wide range of temperatures and related the structural characteristics with the changes occurring in certain mechanical properties.Translated from Poroshkovaya Metallurgiya, No. 12 (360), pp. 72–77, December, 1992.     

Effect of weak shock waves on diamond powders and compacted modifications of boron nitride

Conclusions The effect of weak shockwaves causes extensive compacting of the C_diam, BN_sp, and BN_sp-BN_w powders.In contrast to the static pressures, compacting with the shockwave is accompanied not only by failure but also plastic deformation of the particles.In compacting, agglomerates of particles, subjected to maximum deformation under the given shockwave parameters, form in the volume. The bonding strength between the particles in the aggregates is determined by the degree of their plastic deformation, the density and type of resultant defects, and restoration of the ruptured interatomic bonds on the physical contact areas.In passage of a weak shockwave a substructure forms in the grains and has a beneficial effect on their properties.Deceased.Translated from Poroshkovaya Metallurgiya, No. 7(343), pp. 79–84, July, 1991.     

Electron microscopic examination of the deformation substructure of polycrystalline cubic boron nitride

Translated from Poroshkovaya Metallurgiya, No. 10(322), pp. 40–43, October, 1989.     

Microstructural studies of polytype formation in oxygen-containing aluminium nitride

Oxygen-doped AlN polycrystals were investigated by transmission electron microscope, and different stages of multilayered polytype formation during pressureless sintering were fixed. The decomposition of polytypes was found to take place during quasihydrostatic compression of samples at high temperatures. A model of multilayered polytypes appearing is proposed. The process of polytype formation is represented as isostructural delamination of the AlN-O solid solution at the expense of oxygen extraction on stacking faults, causing the oxygen-rich interlayer formation.     

Substructure of the friction surface of copper and copper-graphite materials

Conclusions In friction at a sliding rate of 40 m/sec and a pressure of 0.1 MPa. a finely disperse mixture of particles of copper and its oxides forms on the surface of pure copper; these particles increase the strength of the surface layer of copper, reduce its wear, but do not prevent bonding processes from taking place.In friction of DGr-5 material at a sliding speed of 11 m/sec under a pressure of 0.1 MPa., surface films consisting of ultradisperse particles of copper and oxides form; the dimensions of the graphite particles are comparable with those of the initial particles. Since the graphite particles cannot extend completely along the prismatic planes to the friction surface and the amount of graphite is insufficient for ensuring the lubricating effect, DGr-5 material is not capable of efficient operation in these conditions.The surface films formed during friction on DGr-10 composite material are characterized by uniform distribution of the graphite particles and consist of ultradisperse copper and fineplate textured graphite with preferential orientation with the basal planes parallel to the friction surface; this results in higher values of the tribotechnical characteristics.Translated from Poroshkovaya Metallurgiya, No. 12(300), pp. 66–71, December, 1987.