Formation of Boron Film on Surface of Austenitic Steel in Scheme of Plasma-Assisted RF-Sputtering of Cathode from Boron

The work is aimed at analysis of the structure and properties of the "film (boron)/ substrate (steel)" system formed on the surface of specimens of AISI 304 high-chromium austenitic stainless steel in the scheme of plasma-assisted RF-sputtering of cathode from boron powder. It has been found that deposition of boron film leads to formation of multiphase multilayer nanocrystine structure, hardness of which exceeds hardness of initial steel by 2.2 times and Young's modulus - by 1.8 times. It has been suggested that the reason for the formation of the multilayer structure is the mutual diffusion of boron, iron and chromium atoms, whereby iron and chromium borides are formed in the boron film layer adjacent to the steel surface and in the steel layer adjacent to the boron film surface. It is assumed that the increase in hardness of the steel surface layer is due to the action of the Orovan mechanism (strengthening with nanosized particles of borides), the Hall-Petch mechanism (strengthening with grain and sub-grain boundaries), the substructural strengthening caused by the formation of the dislocation structure, and the solid solution strengthening associated with the alloying of the γ-iron crystal lattice with boron atoms.