Diffusion Mechanisms in Binary ‘Steel–coating’ Systems Under Long–term High Temperature Exposures

The processes of mutual element diffusion in coating and matrix are the one of significant factors affecting the service life of critical components and assemblies, including products with coatings. These processes render a direct influence on the corrosion resistance and wear of parts, operating at high temperatures in aggressive environments, such as the petrochemical industry. The paper proposes a method for calculating the concentrational distribution of elements in matrix and its coating at high temperature gradients and internal stresses. Concentrational mechanism of diffusion and thermal diffusion by the vacancy mechanism are the dominant mass transfer processes of the coating elements at the binary ‘steel–coating’ system heated to 1173 K (1073–1173 K is the temperature of the pyrolysis under industrial conditions). Both transfer mechanisms are directed into the matrix depth which leads to an intensive relocation of coating atoms to its internal surface layers. The focus of this study was to perform an analysis of the coating concentrational profiles, obtained on the basis of thermal diffusion and vacancy mechanisms of mass transfer taking into account internal stresses in the crystal lattice of matrix.