Some aspects of a metal coating formation of structural components by means of friction stir processing are considered here. The paper provides a simplified description of a thermal field induced either by the process of friction bonding of materials (FSW) or by modifying surface layers of components by means of friction stir processing (FSP). Additionally, a theoretical analysis of mass transport in a high gradient thermal field initiated in micro-areas of materials subjected to FSP and FSW processes are included as well. Regarding the practical aspect of this research the analysis focuses on a Fe-Ni and Fe-Cu diffusion systems in a structural materials. Verification of the presented considerations was carried out for adhesive nickel or copper coatings on S235JR and S355JR low alloyed steels.