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The interaction of titanium, zirconium, and tungsten borides with chromium is studied. It is shown that the process is induced by contact melting involving intensive wetting of borides with interaction products at temperatures much lower than the melting points of components. The temperature dependences of contact angles and the phase constitution of interaction products are analyzed. Chromium vapors that reduce the strength of chemical bonds in the lattice lead to a liquid eutectic phase with low contact angles to the surface of borides and promote the activated sintering of boride systems. It is demonstrated that low-porous (1-2%) borides can form at sintering temperatures lower than the temperature of secondary recrystallization. The dependence of bending and compressive strength on sintering temperature is examined. Conditions for producing low-porous fine-grained materials are determined.

621.762The tribological properties have been examined for composite materials based on binary titaniumchromium boride and titanium nitride under conditions of dry friction over a wide speed range (1-25 m/sec). The materials have good tribological properties, which exceed by almost an order of magnitude those of known materials. Specifications are formulated for materials promising for highspeed friction units. A necessary condition for viability in high-speed friction units is high strength of the adhesion between the films of oxidation products, and another is low tendency for adhesion with the counterbody.A major task in current engineering is to raise the reliability and economy of machines and mechanisms. A decisive part is played by materials for mobile joints. The tribological properties of these govern the wear resistance and power loss, and consequently the working life and performance.During friction, the surfaces are smoothed and working together [1-3], and there are bridges of true contact of interaction between the bodies, which are transformed from the macroscopic level to the microlevel (molecular or atomic), with corresponding reduction in the effects of deformation and increase in the adhesive component of the frictional force. This should be considered primarily in devising materials for high-speed friction units, i.e., the initial components should have low adhesion activity in pairs with the proposed counterbody. Our attention has been attracted by refractory titanium compounds TiB 2 , TiN, and (Ti, Cr)B 2 , since they have little tendency to adhesion with iron alloys, which are the most common counterbodies. For example, the edge wetting angles for iron in contact with titanium boride and nitride exceed 90° [4], and this guarantees inactivity in such contact pairs.We examined the tribology of composites based on refractory titanium compounds intended to operate in air paired with steels under conditions of boundary and dry friction, and also examined the structure and properties of these composites.Composites made on the basis of (Ti, Cr)B 2 were made by sintering porous refractory frameworks under vacuum with subsequent impregnation with copper-nickel alloys. Various antifriction additives were used at the sintering stage (graphite, molybdenum sulfide, and molybdenum selenide). Figure 1 shows typical structures of such materials. The materials have a high level of physicomechanical properties (σ b = 520-640 MPa, HRA = 78-82.5), and they have high density (99-99.5%) and consist in the main of three phases: pale (Ti, Cr)B 2 , darker copper-nickel alloy, and dark-gray inclusions (solid lubricant). They were tested under boundary friction conditions with an M22-M machine with a shaft − insert scheme. The counterbody was quenched steel (St.45).