Thermodynamic conditions for obtaining complex carbide coatings

Abstract

The study examines the thermodynamic regularities of carbide coating formation on steels during complex diffusion saturation processes involving chromium and titanium. The relevance of this research is determined by the need to enhance the wear resistance and durability of machine parts and tools operating under conditions of intensive friction, high temperatures, and aggressive environments. Special attention was given to modeling closed multicomponent thermodynamic systems Cr–Cl–C, Cr–Cl–C–Fe, and Cr–Cl–C–Ti under reduced pressure conditions.

Thermodynamic analysis of the equilibrium state of the reactive environment was performed using the ASTRA software package in the temperature range of 600–1500 K at a constant pressure of 10² Pa. The composition of the gaseous and condensed phases was determined, and the influence of carbon, iron, and titanium content on the partial pressures of transition metal chlorides was studied. It was shown that the carbon content significantly affects the phase composition of chromium carbides in the condensed phase but practically does not change the partial pressures of its chlorides in the gaseous phase. The introduction of titanium was found to lead to the appearance of titanium chlorides in the gas phase and the formation of stable TiC carbide in the condensed state.

Based on the obtained results, conclusions were drawn regarding the sequence of layer formation in complex carbide coatings during chrome-titanium treatment. It was shown that at low titanium content, the formation of chromium carbides predominates, whereas an increase in titanium concentration promotes titaniumization processes with the formation of a TiC layer. The results of thermodynamic modeling were confirmed by experimental studies of coatings on U8A steel, which demonstrated the formation of multilayer carbide coatings with enhanced microhardness. The obtained data can be used to optimize the technological parameters of diffusion saturation processes and to predict the phase composition of protective coatings.