Structurization and Heat Resistance of the U8A Steel with Multi-Component Difu-sion Coatings in the Ti–Cr–Al System

Abstract

Phase and chemical composition, structure, and microhardness of the multicomponent coatings produced by titanium (titanizing) and titanium–aluminum (titanaluminizing) chemical vapor deposition (CVD) of the U8A chromium steel are examined. Both titanizing and titanaluminizing are carried out in powder mixtures of titanium, aluminum, inert additive, and activators at 1050°C for 4 h. It is demonstrated that the proposed methods of saturation result 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. An important content 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 on the basis of chrome carbides. It is demonstrated that the microhardness of multilayer coatings on the basis of chromium and titanium carbides is 16–31.5 GPA and that on the basis of chromium and titanium carbides and intermetallides is 5.8–36 GPа. It is established that, at the temperature of 900°C, the heat resistance of titanium–chromium–aluminum coatings on the U8A steel exceeds that of titanium, titanium–chromium, and chromium coatings.