OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 26 No. 2 2024 Introduction Steels and alloys based on nickel, copper, aluminum and other metals used in industry have low wear resistance, especially under dry friction and abrasive conditions. One of the most widely used techniques to increase wear resistance is to add dispersed solid particles of refractory compounds, i.e. carbides, borides, silicides, into the alloy structure. The material obtained in this way has the structure of a metal matrix composite with dispersion strengthening. Composites with a matrix of iron-based alloys (steel and cast iron) strengthened by titanium carbide particles are of the greatest practical interest. Numerous investigations have been devoted to the study of such composites [1]. Due to the low plasticity of dispersion-strengthened metal-matrix composites, its use as structural materials is limited. Therefore, the metal-matrix composites, including composites with iron-based binders, are used primarily for the parts subjected to severe abrasive wear. The main structural characteristics, which determine the hardness and wear resistance of the composites, are the volume fraction, dispersion and morphology of the strengthening carbide phase particles. The structure of composites depends on the method of its preparation. In casting methods, titanium and carbon are added into the melt, which, during casting and crystallization, form carbide inclusions in the volume of a steel or cast-iron matrix. Lumpy material, i.e. coal coke, pure titanium or titanium-based alloys, is sometimes used to alloy the melt with titanium and carbon [2, 3]. Titanium and carbon powder compacts are more often used, which are placed in a casting mold and poured with steel or cast-iron melt [4, 5]. The carbide phase in the structure of cast composites is represented by round particles ranging in size from 1–3 to 10–15 μm, depending on the concentration of titanium and carbon in the melt and casting conditions, i.e. melt temperature and casting mold, cooling rate, mixing conditions, etc. Attempts to obtain cast details with a surface layer strengthened with carbide particles are described. For this purpose, the surface of the casting mold was covered with a suspension of the titanium and carbon powder mixture. During casting, the covering was impregnated with a melt with the simultaneous synthesis of titanium carbide [6, 7]. Powder technologies for the production of composites with a steel matrix strengthened with titanium carbide particles are used much more often than foundry ones. The most efficient method is sintering of compacts from titanium carbide and steels powder mixtures, which are often replaced with a mechanical mixture of iron powders and alloying elements [8–10]. This method makes it possible to obtain twolayer or multilayer products by sintering of compacts, which consist from layers of various compositions [11]. When titanium carbide powder is replaced by a titanium and carbon mixture, carbide synthesis occurs during sintering, i.e. reactive sintering takes place [12]. Ferroalloy powders are sometimes added to the mixture for pressing and sintering to obtain steel binders [13, 14]. To reduce the porosity of sintered compacts and prevent the growth of carbide grains during isothermal holding, more complex sintering methods are used, requiring specialized equipment: hot pressing [15, 16] or spark plasma sintering [17, 18]. The most effective method for producing “titanium carbide – iron binder” composites is self-propagating high-temperature synthesis (SHS) in reaction mixtures of titanium, carbon and iron (or its alloys). Numerous studies of synthesis products in these reaction mixtures are devoted to the thermokinetic characteristics of the synthesis [19] and its influence on the formation of the composite structure [20, 21]. The dispersion of carbide particles growing from a melt-solution in a combustion wave, its morphology and crystallographic features of growth has been studied [22, 23]. Synthesis has been studied both in the wave combustion and in the thermal explosion modes [24–26]. It is known that the interaction of powder components in reaction mixtures during synthesis intensifies greatly after mechanical activation in high-energy mills [27]. However, our studies have shown that the effect of mechanical activation on the concentration limits of combustion and the initiation of the synthesis reaction in Ti + C + Fe alloy mixtures (high-chromium cast iron or highspeed steel) is much less than expected [28]. The main reason, in our opinion, is the binder metal, which partially blocks the titanium-carbon reaction surface and prevents the carbide synthesis reaction. This can be avoided by replacing two powders, i.e. titanium and binder metal, in reaction mixtures with a powder of an intermediate compound – metal titanide.
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