Microstructural features of the α→β transformation in silicon nitride at high pressures and temperatures

Translated from Poroshkovaya Metallurgiya, No. 12 (360), pp. 50–56, December, 1992.     

Structural features of boron nitride dense phase formation from rhombohedral modification under high static pressure

The real structure of boron nitride (BN) polycrystals after high-pressure treatment was investigated by X-ray and transmission electron microscopy methods. Different stages of boron nitride polycrystal evolution under high quasistatic pressure and high temperature were fixed, involving rhombohedral boron nitride twinning, one-dimensionally disordered structure, 2H, 4H, 3C dense phase formation and 3C-BN recrystallization. A new structural scheme of BN_r-BN_w transition is proposed.     

Changes caused in the composition and structure of flame-sprayed chromium coatings by friction due to contact interaction

The real structure of flame-sprayed chromium coatings in the as-sprayed state and after exposure to friction has been studied by means of electron microscopy, local x-ray spectrum analysis, and Auger electron spectroscopy. The surface layers of the coating were found to become saturated with oxygen under friction and secondary structures with a high defect content formed in those layers. The most stable structures were highly disperse fragmented states formed on the basis of the initial grains as a result of deformation.Institute of Materials Science, Ukrainian Academy of Sciences Kiev. Translated from Poroshkovaya Metallurgiya, Nos. 5/6, pp. 80–85, May–June, 1995.     

Effect of Shock Sintering Temperature and Carbon Content of the WC–Co Hardmetal Anode on the Mass Transfer in Electrospark Deposition

Powder Metallurgy and Metal Ceramics - The paper examines how the shock sintering temperature and carbon content of the VK25 hardmetal and the process time and discharge energy in the electrospark...     

Structure of surface layers of boron carbide after friction in the temperature range 20–1400°C

Conclusions The experimental results show that, starting from 800°C, friction of the boron carbide is characterized by high ductility associated with the formation of planar defects. The results show that the depth of the deformed layer to temperatures of 800–1000°C is determined by the grain size and in the regions of the coarse-grained material the layer is 10–15 m deep which is 3–5 times greater than in the areas of the fine-grained material. The products of wear do not form a continuous layer on the friction surface of the Bi₄C-B₄C pair and are distributed in the form of individual clusters. Friction of this pair in air at temperatures above 600°C is accompanied by the formation of quasiamorphous oxide films.Translated from Poroshkovaya Metallurgiya, No. 8(284), pp. 93–97, August, 1986.     

Crystal defect generation during diffusionless transformations of boron nitride by puckering mechanism

The fine structure of wurtzitic and zincblende BN phases formed during diffusionless transformations by the puckering mechanism was investigated by X-ray diffraction and transmission electron microscopy. The formation of inversion boundaries in prismatic planes of wurtzitic BN was detected. Their appearance is directly connected with the puckering mechanism of transformation. Unlike these defects, the formation of faults in the zincblende phase is a result of plastic deformation which accompanies the diffusionless transformation.     

Physical principles of shock-wave synthesis of superhard phases and their structure

Powder Metallurgy and Metal Ceramics - This paper reviews work carried out at the Institute for Problems of Materials Science, Ukraine National Academy of Sciences, in developing physical bases for...     

Properties and structure features of nanocomposite powders based on SiC

Features of the synthesis of SiC−Si₃N₄−Si₂N₂O composite powders are studied. The characteristics of the powders are examined on the basis of x-ray diffraction, transmission electron microscopy, and Raman spectroscopy. The structure features and mechanical properties of a ceramics formed on the basis of the synthesized powders are also studied. Institute for Problems of Materials Science, Ukraine National Academy of Sciences, Kiev. Traslated from Poroshkovaya Metallurgiya, Nos. 7–8(408), pp. 12–16, July–August, 1999.