FORMATION OF THE STRUCTURE, PHASE COMPOSITION AND PROPERTIES OF ELECTRIC EXPLOSIVE WEAR-RESISTANT COATINGS AFTER ELECTRON-BEAM TREATMENT

Abstract

In the present work, coatings of TiC – Mo, TiC – Ni, TiB2 – Mo, and TiB2 – Ni systems were applied to the surface of Hardox 450 steel by the method of electrospray coating. After that, the electron-beam treatment of the coatings was carried out. It was established that after electro-explosive spraying of the coatings of the systems under investigation, a number of morphological features of the relief are formed on the surface: deformed crystallized microglobules, incrustations, microcraters, microcracks, layers. After the electron-beam treatment of the coatings, microglobules, microcraters and microcracks disappear on their surfaces, a polycrystalline structure is formed, in the bulk of which the structure of cellular crystallization is observed. The roughness of the coatings after electron beam treatment is 1.1 – 1.2 μm. It was also established that the thickness of the layers of electrically explosive coatings modified by an electron beam, depending on the surface energy density, is linear. Its maximum value is observed for the TiB2 – Mo system, the minimum – for the TiC – Ni system, which is explained by their thermophysical properties. In the coatings the following substructures are revealed: cellular, strip, fragmented, subgrain, and also grains with chaotically distributed dislocations and dislocations that form grids. Electron beam treatment of coatings leads to the formation of a composite filled structure throughout the entire section of the remelted layer, forming a more dispersed and homogeneous structure in it than in coatings without electron beam treatment. Dimensions of inclusions of titanium carbide or titanium diboride in molybdenum or nickel matrix are reduced by a factor of 2 – 4 compared with their dimensions immediately after electrospray deposition. Particles of the second phases are found in the volume of molybdenum or nickel grains and at the boundaries: titanium carbide or titanium diboride. They have a rounded shape and can be divided into two classes in size: 1. particles of initial powders with dimensions of 80 – 150 nm, not dissolved in the irradiation process; 2. particles released during crystallization of the melt with dimensions of 10 – 15 nm. The basis of the structure formation in electric explosive powder coatings is the dynamic rotation of the sputtered particles, which form a vortex structure both in the coating and in the upper layers of the substrate. Formed coatings have increased performance properties: nano- and microhardness, a modulus of elasticity of the first kind and wear resistance in conditions of dry sliding friction.