Structure and Properties of the Steel Surface Layer Containing Nitrides and Silicides of High-Melting Metals Formed by Electron-Ion-Plasma Method

摘要

The work is aimed at discovering the regularities of modification of the elemental and phase composition, defective substructure, mechanical and tribological properties of carbon steel subjected to combined processing in a single vacuum cycle, including the deposition of high-melting metal and silicon coatings and irradiation with an intense pulsed electron beam to obtain a surface layer with improved strength and tribological properties. Thin (1 µm) films of silicon and niobium sequentially were deposited on the polished surface of 5135 steel samples on the “COMPLEX” installation, developed in the laboratory of plasma emission electronics HCEI SB RAS, included in the list of unique installations of the Russian Federation (“UNIKUUM” complex http://ckp-rf.ru/usu/434216/). The deposition of a silicon film was carried out by magnetron, and niobium films – by electric arc methods with plasma assistance. Then the resulting system “film/substrate” was irradiated with a pulsed electron beam in the mode of co-melting with the surface layer of steel ((20–50) J/cm2, 200 µs, (3–30) puls.). It was found that the maximum hardness of the surface layer of the modified steel, is equal to 9600 MPa (3.3 times higher than the hardness of steel in the initial state), is achieved at a 200 µs beam pulse duration, an energy density of 50 J/cm2, and a number of pulses of 3. It is shown that the minimum wear parameter of the modified steel is k = 2.83·10−6 mm3/N×m, fixed for a 200 µs beam pulse duration at an electron beam energy density of 50 J/cm2, what is more than 15 times less than the wear parameter of steel in the initial (ferrite-pearlite structure) state. It is shown that the high strength and tribological properties of steel, revealed upon irradiation of the “film/substrate” system with an electron beam (50 J/cm2, 200 µs, 3 pulses), are due not only to the high content of the strengthening phase (niobium silicides with the composition Nb_3.61Si_0.39, intermetallic compound Nb₀₈Fe₀₂, niobium oxide NbO₂ and silicon carbide SiC) particles, but also with a relatively large thickness of the hardened layer, reaching 30 µm.