O. N. Grigor’ev

Synthesis and properties of ceramics in the SiC — B4C — MeB2 system

The effect of impurities and additives of titanium and zirconium borides on the structure and mechanical properties of SiC — B4C ceramics over a broad temperature range has been investigated. The ceramics was fabricated by hot pressing without a protective medium. Introduction of borides is accompanied by improvement in all the studied mechanical properties at room temperature, and the nature of hardening of the ceramics is practically independent of the type of SiC powders used. At high temperatures, the mechanical behavior of the ceramics is determined by the impurity composition: the ceramics obtained using abrasive powders loses strength beginning at 600°C, while using powders with decreased impurity content makes it possible to preserve the strength of the material up to a temperature of 1400°C.

Friction properties of composites of the system TiN−AlN. I. Effect of structure and phase composition of friction and wear of materials of the system TiN−AlN

The tribological properties of ceramic composites of the system TiN−AlN are studied in the concentration range 10–90% AlN. It was found that materials which contain 25, 50, and 75% AlN have a low friction coefficient. Their rate of wear when paired with steel is neglible—2.9–6.0 μm/km (the wear rate of a steel-steel 024 couple is 1000 μm/km). Thin oxide films are formed during friction at high velocities and pressures. These films have relatively high adhesion with respect to materials of the TiN−AlN system and relatively low adhesion with respect to steel. The films may act as a solid lubricant, thus reducing the friction coefficient and wear. This is particularly true of the materials 25% TiN−75% AlN and 50% TiN−50% AlN.

Directionally solidified eutectic of the B4C - ZrB2 system

An investigation was made of reactions in the Zr - B - C system. The existence of a eutectic in the quasibinary section B4C - ZrB2 was confirmed. A directionally solidified eutectic alloy was obtained by zone melting. Its composition was precisely determined as (mol. %) 71.5 B4C, 28.5 ZrB2. The effect of melting parameters on the eutectic structure was studied.

Phase interaction between ZrB2–SiC composite ceramics and oxide melts

The paper studies the mechanism of interaction between ZrB2–ZrSi2–SiC composites and dross-type oxide melts formed during the combustion of low-reactive carbons containing oxide rocks up to 30–40 vol.%. It is established that silicon carbide from the surface layer of the composite interacts with iron oxides to form spherical precipitates of the FeSix phase at 1350–1550°C in the wetting process and in contact with the dross during 10–50 h. At the composite–dross interface, a thin (~7.5–30.0 μm) layer of ZrO2 and SiO2 oxides forms (depending on the amount of SiC and ZrSi2) and serves as a protective film preventing the composite ceramics from corrosion in the oxide melts. The optimum composition of the ZrB2–ZrSi2–SiC ceramics that can be used as corrosion-resistant in oxide melts is determined.

Ceramics and Cermets Based on Nonoxide Refractory Compounds

The papers presents results of studies focusing on the development and characterization of ultrahigh-temperature structural ceramics, ceramics with high wear resistance and impact penetration resistance, and cermets and coatings based on nonoxide refractory compounds. The phase and structure formation of the materials is studied in interrelation with their mechanical and service properties. The materials are intended to perform as wear-resistant, shock-resistant, and structural parts (at temperatures above 1600°C in corrosive environments) for machines and units in various engineering fields.

Riction properties of composite materials of the system TiN - Ain. II. Effect of oxide films on friction and wear of a ceramic material — Steel system

Friction and wear are studied for materials of the system TiN — AlN preliminary oxidized at 800–1100°C. It was established that thin oxide films containing Al2TiO5 and α-Al2O3, that promote a decrease in frictional wear, form on the surface of composite materials of the system TiN — AlN. Our assumptions are confirmed that the improvement in tribological properties of TiN — AlN composites is caused by forming oxide screening layers that prevent direct contact between the ceramics and steel counter-body. At high rates (V=16 m/sec) and pressure (P=2.0 MPa) the oxide films form more rapidly.

Gradient Laser ZrB2–MoSi2 Coating on Graphite

A high-temperature ZrB2–MoSi2 coating on graphite is produced by pulsed laser melting (in air) of a graphite sample with powder layers pre-deposited on the working surface. It is demonstrated that laser melting is accompanied by an intensive phase formation in the layers and at the interface. The main phases of the surface are: ZrB2, MoSi2, Mo5Si3, and ZrC. It is demonstrated that the coating forms with the liquid phase reinforced with ~1 μm thick fibers. It is characterized by a gradient change in the composition towards the substrate: the content of ZrC increases and the content of ZrB2 decreases towards the graphite substrate. Such a change in the composition leads to higher adhesive strength of the coating.

High-temperature laser coatings of the ZrB2–MoSi2 system on graphite

Coatings of the ZrB2–MoSi2 system on graphite (≤ 50 μm thick and 14–15 GPa in hardness) have been produced by pulse laser melting in air of two-layer powder coating with sublayers based on ZrB2 with additions of ZrSi2 and SiC. Different coating structures: eutectics of the ZrSiO4–SiO2 system based on zircon or a structure of micron-thick fibers of composition Zr(Mo)B2 are formed depending on the sublayer composition, which controls the coating heat conductivity and accordingly, the crystallization rate of the bath of melt. The prospects of this line of investigations are the improvement of a laser technology of the deposition of high-temperature coating using continuous wave lasers.