Structurization and High-Temperature Oxidation Resistance of U8A Steel with Ti–Cr–Al Multi-Component Diffusion Coatings

Abstract

The phase and chemical composition, structure, and microhardness of multi-component coatings produced by tetanizing (titanium) and titanaluminizing (titanium–aluminum) chemical vapor deposition (CVD) of U8A chromium steel are examined. Both titanizing and titanaluminizing were carried out in powder mixtures of titanium, aluminum, inert additive, and activators at 1050°C for 4 h. It is demonstrated that using the proposed saturation methods results in the formation of multilayer coatings of: (i) chromium and titanium carbides after titanizing; (ii) chromium and titanium carbides; titanium, aluminum, chromium, and iron intermetallides after titanaluminizing. A high concentration of iron, chromium, titanium, and aluminum is discovered on the external surface of the titanaluminized coatings. Both Fe and Cr can be provided by a chromium layer based on chrome carbides. It is demonstrated that the microhardness of multilayer coatings based on chromium and titanium carbides is 16–31.5 GPa and that based on chromium and titanium carbides and intermetallides is 5.8–36 GPa. It is established that, at a temperature of 900°C, the hightemperature oxidation resistance of titanium–chromium–aluminum coatings on U8A steel exceeds that of titanium, titanium–chromium, and chromium coatings.