ABSTRACT

Experiments on deposition of barrier and heat-resistant layers were conducted. As the barrier layer (BL) use was made of ZrN that was deposited on carbon–carbon composite material (CCCM) by the method of ion-plasma sputtering. Heat-resistant coatings were applied by the method of atmospheric plasma spraying. A series of samples with the following compositions of heat-resistant layers were obtained in the work: (1) 92 wt.% ZrO₂ + 8 wt.% Y₂O₃; (2) (92 wt.% ZrO₂ + 8 wt.% Y₂O₃) + 10% HfO₂; (3) La₂Zr₂O₇; (4) 20% (ZrO₂ + 8% Y₂O₃) + 80% MoSi₂, and (5) 10% (ZrO₂ + 8% Y₂O₃) + 90% MoSi₂. Also presented in the work are the results of scanning electron microscopy, as well as phase and elemental analysis of the coating obtained. It has been elucidated that the sample with coating of composition (1) has a fine-grain structure pierced by a net of cracks; the sample with coating of composition (2) has only local cracks, whereas that with coating of composition (3) has a large-grain structure with the absence of cracks. The sample with coating of composition (4) also has no cracks and the structure consists of fused particles. This is due to the presence of thermal stresses in the coating caused by the presence of various polymorphic modifications of zirconium dioxide. To stabilize one of these modifications and reduce the stresses that lead to cracking of coating, additives of titanium oxide (2) and of lanthanum oxide (3) were used. The presence of the nanomodified additive HfO₂ in amounts of 10 wt.% in coating of composition (2) did not lead to a decrease in thermal stresses, which is seen on micrographs. It is shown that in the samples with coatings of compositions (2) and (3) the microstructure differs substantially, from which the conclusion was drawn that the nanomodifying additive of yttrium oxide increases the plasticity of coating and prevents the formation of cracks. The samples were subjected to testing for heat resistance in an oxygen–acetylene torch flow for 20 s at a temperature 2100°C. It has also been established that coatings of compositions (4) and (5) have excellent operating characteristics and that with increase in the concentration of MoSi₂ in a coating, the porosity decreases, the structure of the coating becomes finer, with the average size of the structural component decreasing by 75 nm. Thus, it was possible to attain the self-healing effect with simultaneous stabilization of the monoclinic phase.