Regularities of structure and properties modification of the steel surface layer as a result of high-cycle high-speed melting of the “film (Si + Nb) / (steel) substrate” system by an intense pulsed electron beam

Abstract

Surface alloying is a promising method for improving the service characteristics of machine parts and mechanisms. The aim of this work is to analyze the patterns of evolution of the elemental and phase composition, the state of the defect substructure of the surface layer of carbon steel subjected to multi-cycle treatment (the number of cycles was varied from 1 to 5), which combines the formation of a film / substrate system and irradiation with an intense pulsed electron beam. Silicon and niobium are used as alloying elements. It has been established that irradiation of the system “film (Si + Nb) / (steel 5135) substrate” at an electron beam energy density of 20 J / cm2 leads to the formation of a multiphase high-speed cellular crystallization structure in the surface layer. The size of the crystallization cells varies from 180 nm to 520 nm, reaching the maximum size after 3 cycles of deposition-irradiation. The surface layer of steel is quenched during processing to form a martensitic structure. It was found that the Nb5Si3 is the hardening phase of the modified layer, the maximum amount of what (up to 9 wt%) was revealed after three processing cycles. It is shown that the maximum hardness of the surface layer of modified steel 5135, equal to 9300 MPa (3.2 times higher than the hardness of steel 5135 in the initial state), is achieved after 3 cycles of deposition / irradiation. The wear resistance of steel at this processing mode increases more than 90 times. It has been suggested that the hardening of steel surface layer is due to the formation of a quenched structure and the release of niobium silicide particles.