621.762We have analyzed the process of structure formation during pressing of copper-tungsten composites. We have established the effect of the amount of the rigid phase (tungsten alloy) in the mix on the pattern of structure formation and the properties (Young's modulus and bending strength) of unsintered articles made from heterogeneous powder material based on copper. We have experimentally established that despite the substantially higher porosity and high volume fraction of the rigid phase, specimens of composition Cu − 50% W alloy have higher green strength and higher modulus of elasticity. Analysis of the true stress − true strain curves of the porous cold-pressed articles compared with the results of microstructural studies allowed us to determine the effect of the structure formation pattern on the strength properties of articles made from copper-based powder material containing tungsten alloy. By studying the structural features of the porous articles, we determined the mechanism for creation of interparticle contact which determines the strength characteristics of unsintered compacts of heterogeneous composition based on a plastic matrix with different amounts of the rigid phase.
UDC 621.762The structure of hot-forged R6M5K5-20% TiC carbide steel is examined. In comparison with sintered carbide steels, it has no transition ring zone at the interface between the carbide grain and the base metal. The matrix alloy has a fine structure and the texture of grains is perpendicular to the forging force.Carbide steels stand out among many iron-based wear-resistant materials produced with powder metallurgy methods. These are composites commonly based on alloyed steels with fine inclusions of transition metal carbide particles (mainly titanium carbide) with a mass fraction of 20 to 70% [1-3]. The volume fraction of the refractory phase in carbide steels is much higher than that in tool steels but is lower than in conventional hard alloys. Hence, carbide steels are intermediate in properties. In this regard, they can be subjected to all types of mechanical treatment after annealing. When hardened and tempered, carbide steels exhibit high hardness (to 86−88 HRA) and wear resistance, which in many instances compare well with those of conventional hard alloys [3].In the commercial production of parts from such materials, the process includes charge makeup (grinding of mixed titanium carbide and metal powders), pressing of the billets, and their sintering above the solidus temperature of the metal component (liquid-phase sintering) [1,2,4,5].An alternative to liquid-phase sintering to produce carbide steels is to impregnate a carbide skeleton with steel melt. Materials produced in this way have, as a rule, higher density and higher fracture toughness than those obtained in liquid-phase sintering [1]. The method involves the formation of a carbide skeleton, its preliminary sintering, and subsequent impregnation with metal melt. The billets impregnated under optimal conditions retain their shape and (as distinct from liquid-phase sintering) original dimensions; moreover, their surface has no swelling or lapping.Examining the structural parameters of materials produced by liquid-phase sintering and impregnation of a porous carbide skeleton with melt shows [1, 3] that these processes promote high density of the billets and cause the structure to become coarsened and carbide and austenite grains to grow, which deteriorates mechanical and operating properties. Therefore, to obtain low-porous structures, the relevant processes should not use temperatures at which a substantial amount of the liquid phase exists, in particular, methods based on hot shaping of porous billets.
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