Oleg N. Grigor'ev

New structural unidirectional-fiber material

Structural basaltic materials are analyzed to establish the relationship of their structure to strength and fracture resistance. It is shown that their strength is determined by the size of initial crack-like defects, and fracture resistance by the amount and extent of weak boundaries that are perpendicular to the growing main crack. Samples of one-component unidirectional basalt fiber material of channel structure were produced by hot pressing. It is shown how temperature and time under pressure influence the structure and fracture behavior of the material.

Wear-Resistant Layered Electrospark Coatings Based on ZrB2

We have studied the composition and tribological parameters (coefficient of friction and wear rate) of coatings obtained in electrospark alloying (ESA) of steel 45 with the composite ceramic ZrB2 – SiC – B4C based on zirconium diboride. We have shown that layer-by-layer electrospark alloying using Ti – Al – N composites to form an undercoat reduces the coefficient of friction of the coating down to 0.12-0.20 while maintaining a rather low wear level (7-11 μm/km). We have analyzed the effect of the composition of the secondary structures which are formed during tribo-oxidation under dry friction conditions.

Structure and Properties of Ceramics Based on Tungsten and Titanium Borides and Boron Carbide

The W2B ― TiB2 ― B4C ceramics studied were hot-pressed from composite powders synthesized by thermal reduction of boron carbide. The resulting materials have a skeleton structure with a boron carbide binder when the B4C content is high and an inclusion-matrix structure when the B4C content is low. The grain size varies from 5 to 20 μm, depending on the preparation conditions. The composite has a hardness of 17.5-20 GPa with a strength in the range 500-1000 MPa.

Production of laminated ceramic composites based on AlN and B4C and study of their properties

The properties of laminated ceramic systems, especially those with low-strength bonds, are discussed. It is shown that residual stresses, which depend on the physical and mechanical characteristics (such as strength, thermal expansion coefficient, thickness, intensity of interfacial interaction) and structure of the main layers and interlayers, affect the fracture behavior of composites. Laminated materials with low sensitivity to defects and strength as high as that of the main layer were produced using a number of oxygen-free refractory compounds.

Phase Formation in Sintering of Materials Based on Silicon Nitride with Li2CO3 and AlN Additives

We have studied the phase formation processes occurring in sintering of materials based on silicon nitride with lithium carbonate and aluminum nitride or Al powder additives. We have studied samples of different compositions that were sintered at 1450, 1550, and 1750°C under a nitrogen atmosphere. We have established that the phase composition depends on the sintering temperature, the composition of the starting charge, and also the amount and the nature of the Al-containing additives.

Study of Phase Formation Processes in the Systems Li ― N, Si3N4 ― Li3N, Si3N4 ― Li3N ― Y2O3

We have studied phase formation processes in the systems Li ― N and Si3N4 ― Li3N. By nitriding lithium powder at temperatures of 400-600°C, we obtained lithium nitride Li3N with a composition approaching stoichiometric. In the system Si3N4 ― Li3N in the temperature range 300-1300°C, the ternary compounds Li8SiN4 (500°C), Li5SiN3, Li2SiN2 (900°C), and LiSi2N3 (1300°C) are formed. The studied properties of the hot-pressed composite material of the system Si3N4 ― Li3N ― Y2O3 allow us to provisionally assign it to the class of solid electrolytes.

Effect of Lithium Carbonate on the Structure Formation of Ceramics Based on Si3N4

Structure formation in the system Li2CO3 ― Si3N4 both during heating in the powder state (500-1450°C) and also during specimen sintering (1450-1750°C) is studied. The most active formation of binary Li ― Si nitrides (LiSi2N3, Li2SiN4, Li8SiN4) is observed at 1450-1550°C. With a controlled sintering temperature and the amount of added Li2CO3 it is possible to prepare materials based on silicon nitride with a prescribed phase composition and corresponding properties.