M. S. Koval’chenko

Hot pressing of powders of refractory compounds and materials based on them

A brief summary is given of results from research initiated by G. V. Samsonov as regards the theory and practice of hot pressing for refractory-compound powders and materials based on them.

Effect of prior heat treatment for commercial-grade aluminum nitride powder in gas atmospheres and activating additions on the structure and properties of hot-pressed ceramics based on it

The effect of carbon-containing additions and prior heat treatment in hydrogen and nitrogen for commercialgrade AlN powder on the chemical composition, structure, and also some physicomechanical properties of hot-pressed ceramics based on it are studied. It is shown that hot pressing occurs mainly in the solid phase. The fracture mechanism for hot-pressed ceramics varies from intercrystalline (using unprocessed AlN powder) to predominantly transcrystalline, the grain size of the basic phase decreases, and thermal conductivity and strength parameters increase.

Dynamics of mechanical action on materials. X. Hydraulic loading of a system

The movement of an open mechanical system with one degree of freedom modelling uniaxial tension of a viscoelastic strain hardenable body in a machine with a hydraulic drive that generates a variable force and is simultaneously a damping element of the system is analyzed. It is demonstrated that transient movement of the system in question corresponds to a fourth order non-autonomous dynamic system that has stable periodic and aperiodic solutions in relation to its control parameters. In view of a marked decrease in viscous resistance of the system caused by the presence of a hydraulic drive aperiodic damping is typical for the transient process. It is shown that a system with a hydraulic element differs markedly from a system that does not contain such an element.

Dynamics of mechanical action on materials. IX. Preset movement of a system

The dynamics of an open mechanical dissipative system involving a viscoelastic strain hardenable body above and below its elastic limit is considered when the force generated with movement is governed by the kinematics of a machine with preset movement. The dynamic origin is clarified for the nonlinear part of the tensile curve beyond the elastic limit for a viscoelastic body to which “nonliear elasticity” is attributed. It is demonstrated that it arises as a result, a transient relaxation process. On completion of this process a force is established within the system governed by viscous flow of the body and corresponding to its yield point. As a result of the change in controlling parameters and the effect of a delay a bistable state arises for the system beyond the elastic limit leading to its macroscopic acoustic activity.

Increasing the wear resistance of surface layers of high-speed steel by electric-spark alloying and laser treatment

How the combined action of high-energy spark alloying and laser treatment affect the wear resistance of high-speed steel cutting tools has been studied. That action has been found to form a strengthened layer of composite refractory compounds on the tool surface, thus making it hard and wear-resistant, and create a protective barrier that reduces the adhesive interaction of the cutting tool with a chip. The tribological properties and the durability of the cutting tool can be enhanced by alloying the surface layer with elements and compounds that form stable oxides tightly bonded to the substrate.

Effect of the electrospark alloying regime on the durability of high-speed steel R6M5K5 cutters

The effect of electrospark alloying with refractory compounds based on WC, TiC, TiN, and TiB2 on the mechanical and service properties of high-speed steel R6M5K5 cutters was investigated. Increasing the electrospark discharge energy by increasing the current strength to 3 A, and the specific alloying time to 1.2–1.8 Msec/m2, increased the alloyed layer depth, but decreased the microhardness. Further increase of alloying time did not produce further increase in layer depth. The optimal regimes of electrospark alloying were determined from durability tests of the hardened cutting tool. The greatest increase in durability (by 1.3–1.4 times) was obtained at I=1.5–2 A, τ=0.9–1.5 Msec/m2, at which values the optimal combination of hardness and coating depth was attained.

Effect of physicochemical treatment of initial powders on the properties of sintered ceramics in the Si3N4-Al2O3-SiO2-Y2O3 system. II. The structure and properties of sintered ceramics

In the first report [1], we described the methods and results of examining the properties of initial powders, and also the results of modifying these powders by means of different physicochemical interaction effects. In the second report, we examine the dense ceramics based on modified powders, and also generalize the data, obtained these investigations, on the role of the composition and state of the surface of the initial silicon nitride powder and the formation of the final properties of the Si3N4-Al2O3-SiO2-Y2O3 ceramics.