G. A. Bovkun

Relationship between Erosion and Mechanical Characteristics of Fine-Grained Hard Alloy WC – 16% Co Obtained by Solid-Phase and Liquid-Phase Consolidation. Part 1. Erosion Resistance

We have studied the erosion characteristics of hard alloys under electrospark alloying conditions, and the relationship of such characteristics with the physical and mechanical properties. WC – 16% Co alloys were obtained by conventional sintering under vacuum in the temperature range 950-1350°C, and by sintering followed by high-energy pressure treatment at the same temperatures. We have shown that the erosion resistance depends ambiguously on the porosity and bending strength but is quite clearly connected with the crack resistance and the electrical resistivity which in turn is determined by the quality of the interphase and intergrain boundaries. We have refined the structural dependence of the erosion resistance of hard-alloy electrodes. This dependence is manifested to the same extent as the structural dependence of the electrical resistance.

Structure and Certain Properties of Hot-Pressed Boron Carbide-Based Ceramic with Calcium-Silicon Additive

The influence which the composition of powder mixtures, the treatment conditions which the mixtures are subjected to, and the conditions under which the hot-pressed composite materials B4C – (5-10 mass%) calcium-silicon are fabricated exert on the structure, nature of failure, and mechanical properties of these materials is investigated. Optimum properties are possessed by material containing 10 mass% of addition. It is shown that the structure, morphology, and dispersivity, as well as the nature of the distribution of the components that are added to the composite material (secondary phase) vary as the temperature of hot pressing changes. Maximal mechanical characteristics of the composite material (σbend = 560 MPa, K1c = 4.7 MPa·m1/2, HV = 37 GPa) are attained at hot-pressing temperatures in the range 2000-2100°C.

HIGH-TEMPERATURE FRICTION OF BORIDES OF GROUP IV-VI METALS

This work is devoted to a study of the characteristics of friction of transition metal borides in heating to 1200~ in vacuum and to 1000~ in air. Samples of TiB2, ZrB2, CrB2, Mo2Bs, W2Bs, and (Ti,Cr)B2 were prepared from technical purity powders of Donetsk Plant for Chemical Reagents by hot pressing in graphite molds~ The residual porosity of the samples was 2-5% and the grain size did not exceed 15 ~m.

ANTIFRICTION COATINGS ON ALUMINUM AND ITS ALLOYS FORMED BY ELECTRIC SPARK ALLOYING FROM POWDER MATERIALS

The effectiveness of the method of ESA with powder materials for the reinforcement of aluminum and its alloys may be linked with several factors. First, powder particles introduced into the electrode gap (EG) initiate discharges at a greater distance between the electrodes, and increasing the EG brings about a redistribution of the discharge energy in the anode-EG-cathode system such that the proportion of energy liberated on the electrodes decreases, while that liberated in the EG increases [5]. Secondly, the presence of powder particles in the EG results in the formation of a multichannel electric discharge structure [6], which divides a single erosion crater into a multitude of small craters. With the simultaneous decrease in energy liberation on the electrodes, the powder particles entering the discharge channel experience comminution with rapid melting and evaporation pulses, so that material transport to the basis is effected in the vapor, liquid, and solid phases. Relief forms mainly with the participation of the liquid phase because solid-phase particles seldom attach themselves firmly to the cathode surface. An electron microscopical examination of the microrelief on an aluminum cathode revealed long streaks of molten powder material and spreading of the liquid phase over the surface (Fig. i). Under these conditions the erosion of both electrodes was considerably reduced, with the anode being practically unconsumed and the volume erosion of the cathode being much smaller than the volume of the coating-forming powder material transported onto it. The effectiveness of the process of ESA of aluminum and its alloys was assessed in rubbing tests on coatings. A study was made of the effect of composition of the powder mixtures on the structure, thickness, hardness, and wear resistance of coatings. In these tests copper,