Development of predictable secondary structures in materials for high-temperature bearings

Abstract

621.762The composition of secondary structures that develop on the surface of high-temperature composite materials based on steel R6M5F3 scraps with a CaF 2 admixture is investigated under friction at a slip speed of 1 m/sec, load of 7 MPa, and heating temperature of up to 600°C in air. The possibility of predicting and controlling functional properties of bearing materials by selection of initial components that provide for development of friction films of the required thickness and composition is demonstrated.Researchers attempting to increase service requirements of newly engineered entities are faced with the problem of creating new tribotechnical materials with a prolonged service life, while providing energy-and materialresource savings. Methods of powder metallurgy have no alternative for solution of the indicated problem. Nevertheless, powder technology is seeing very little exploitation of its potential, especially in the creation of bearing materials.An insufficiently complete understanding of processes that occur on the friction surface of materials during service under extreme conditions (high temperatures and velocities, heavy loading, and aggressive media), and their effect on the wear resistance of the materials is one of the main obstacles in this path. Continued success in the development of new anti-friction materials and provision for their optimal operating conditions will therefore depend on profound comprehension of the mechanism responsible for friction and wear under the influence of external factors and its accompanying phenomena.Complex mechanical, thermal, and physico-chemical processes, which lead to substantial variations in their properties, occur in the surficial layers of materials subject to friction [1,2]. Here, the wear resistance of the materials is determined not so much by their initial characteristics as by the properties of the films that form on their surfaces. Since the laws established in many studies for friction processes are, as a rule, special in nature, and are valid only within narrow bounds of a specific experiment, study of the above-indicated phenomena, and, primarily, the condition of the surface layer which exerts a decisive influence on the performance of friction couples, is of greatest interest.Kragel'skii [1] and Fedorchenko and Pugina [2] have established that the character and properties of the films that form directly on contacting surfaces (so-called secondary structures) predetermine the serviceability of the antifriction material and friction subassembly as a whole. Secondary structures that form when powder materials are subject to high-temperature friction where liquid lubricants are not serviceable, and solid lubricating components are added to the mixture have not, however, been well understood until now.New high-temperature powder anti-friction materials, for the creation of which wastes from tool, ball-bearing, and die production have come into widespread use as a base [3][4][5], have covincingly demonstrated the steadily high tribotechnical pr...

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