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669.28:621.793.79

STRUCTURE AND PROPERTIES OF A SILICIDE-CARBIDE PROTECTIVE COATING ON CARBON-CARBON COMPOSITES I. B. Gnesin1 and B. A. Gnesin1 Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 6, pp. 39 – 43, June, 2020.

Heat resistance and microstructure properties of a prospective multilayer protective coating on carbon-carbon composite materials are studied. Thermomechanical compatibility of a coating with base material, its thermal stability, thermal shock and cracking resistance are evaluated.

Key words: carbon-carbon composite materials, protective coatings, oxidation resistance, silicides, carbides, phase transformations, heat resistance.

coatings [12], an increase in adhesion by forming a more developed coating – base boundary [13], and introduction of strengthening components into a coating [14]. However, so far this problem has not been resolved and therefore a search for processes making possible to reduce coating cracking currently remains an important scientific task. It is necessary to develop existing and to look for new methods for reducing the unfavorable effect of a difference in LTC for a base and coating. Within the scope of research conducted in the Institute of Solid Physics of the Russian Academy of Sciences an approach has been developed including creation of accommodation layers within a coating [15]. The main function of these layers is a reduction in thermal stresses arising during thermal cycling, and also making crack growth difficult within a coating. This is achieved due to introduction into a coating of fine carbide phase and carbon fibers alongside silicides. In this case non-heat resistant phases (carbides and carbon fibers) should be isolated within a coating from the external medium by heat-resistant silicide phases. In our previous work [15] it was established that introduction of carbon fibers in the form of carbon cloth facilitates a significant reduction on model coating cracking. However, the question of forming a heat-resistant layer of a coating over the accommodation layer was not considered in this work. In the present study development of approaches proposed in [15] is continued. Apart from forming an accommodation layer, the possibility has been determined of forming a layer with increased heat resistance by adding silicon carbide particles together with refractory metal silicides into a coating surface layer.

INTRODUCTION Contemporary carbon-carbon composite materials (CCCM) exhibit a unique combination of properties: low density, high strength, creep resistance, crack resistance, and also a capacity to retain properties up to high temperature [1, 2]. Due to this CCCM have considerable potential in aviation and space technology. However, for these materials there are also disadvantages: they are subject to marked oxidation starting at a temperature of about 500ºC [3]. In view of this for effective operation in an oxidizing atmosphere at high temperature (especially above 1000ºC) CCCM require protective coatings. The majority of existing protec