Formation of ultradispersed state of surface layers of the steel alloyed with metal ions in the mode of melting by plasma jet

A review of the methods for surface alloying of steel and features of ultradispersed- layers' formation by doping under melting mode is performed. New results of the investigation of structure, tribological, physical, and mechanical properties of iron and 40Kh structural steel treated by plasma current under conditions of melting with simultaneous alloying with tungsten or molybdenum are presented and analysed. Using the methods of Rutherford ion backscattering, scanning electron microscopy, X-ray spectral analysis, X-ray phase analysis, it is shown that, after pulsed plasma treatment, a thin layer with a thickness up to 5 microns with regular placement of the crystallites saturated with nitrogen, carbon, and alloying element is formed on the surface of the material. The formed structure as a whole has a needle and banded arrangements. Layer located at a larger depth with a thickness of about 40 ?m is composed of grains with micro- and nanostructure. The study of treated samples shows that the wear resistance of hardened surface is by 2-5 times higher than that of the original surface. Measuring of friction coefficient, using scratch device after treatment and doping, shows a decrease of friction coefficient (from 0.5-0.7 for untreated samples to a value of 0.4 after treatments) for almost entire depth of abrasion.