Використання боридних і силіцидних покриттів у ДВЗ: технологічний аспект

Abstract

The main regularities of the process of forming on refractory metals the single-phase, multi-phase, multi-layer composite coatings with high heat resistance and durability are examined in the article. A study of boride coating on refractory metals was conducted, which showed that a single-phase coating is formed on metals that possesses good adhesion to the base. Based on the results of X-ray phase and micro-X-ray spectral methods of analysis, the formation of a monoboride phase on molybdenum and tungsten and a boride phase on niobium and tantalum was revealed. A study of the effect of temperature on the process of diffusion silicification of refractory metals was carried out, which showed that in the range of 950–1100 0С, a single-phase coating is formed, which consists of disilicides of МеSi2 metals. A further increase in the temperature of the saturation process was found to lead to a sharp increase in the thickness of the silicide layer. It was proved that an effective diffusion barrier is the boride phases of refractory metals, which ensure the stability of the diffusion part of the multicomponent coating. The boride phases were determined to be more stable than silicide phases in relation to the metal base. Due to the formation of silicoboride phases at the border of boride and silicide layers, high stability of the borosilicide coating is ensured. The presence of penetrating impurities in the metal matrix leads to poor protection of the oxide film of the diffusion coating and, as a result, to low durability. A mechanism for the transfer of penetrating impurities from the depth of the metal to the boundary of the powder medium is proposed. The obtained borosilicate-saturated metal technological parameters allow forming a diffusion coating with a fine-grained structure on refractory metals. To ensure high protective characteristics, the formation of the layered part of the coating should be further researched.