ELECTRIC ARC COATINGS WITH A COMPLEX OF IMPROVED PROPERTIES FOR REPAIRING AND HARDENING OF MINING MACHINE PARTS

Purpose. Research and analysis of the possibilities of using electric arc coatings with improving properties in the repair of machines and mechanisms for mining industry. 
Methodology. The porosity of the obtained electric arc coatings was studied using computer metallography. The hardness was determined on a Vickers-type device. The thermophysical properties of the coatings were studied using the dynamic calorimeter method. The adhesion strength of the coatings to the substrate was determined by the method of "pulling the pin". Determination of wear resistance was carried out on the SMC-2 friction machine according to the "roller-block" scheme in conditions of limited lubrication. The determination of coherent x-ray scattering regions to estimate the size of the substructure of the coating material was carried out by x-ray diffraction analysis on the DRON-3 installation. 
Results. An electric arc sprayer has been improved, which makes it possible to improve the quality of composite coatings by increasing the particle velocity in a high-temperature heterophase jet and reducing its opening angle, which leads to an increase in the CMM during spraying from 0.63 to 0.74. At the same time, the increase in the hardness of the metal matrix in the composite electric arc coating is 21%, their adhesion strength to the base increases by 26%, wear resistance is 6.9 times compared to the unfilled coating. The optimal amplitude-frequency parameters of the electric pulse action during electric arc spraying of the SV-08G2S wire (pulse frequency – 6.5 kHz, amplitude – 5 kV) are determined, which provide an increase in hardness up to 35%, adhesion strength to the substrate up to 30% and wear resistance of coatings 1.7 times due to grinding and acceleration of the sprayed particles. The optimal temperature-time parameters of pre-recrystallization heat treatment are established, which provide a further increase in the hardness of coatings due to the grinding of subgrains to the nanoscale size inclusive. The possibility of thermal stabilization of the polygonization substructure of electric arc coatings obtained by spraying 12X18N10T wire by their additional plastic deformation is shown. 
Originality. The electric arc coating method was further developed by improving the design of the spray head, which made it possible to increase the material utilization rate during their spraying and physical and mechanical, as well as operational properties. The regularities of the influence of electric pulse action on the microstructure and physical and mechanical properties (hardness, density, adhesion strength, thermal conductivity, wear resistance) of electric arc coatings are established. The process of pre-crystallization treatment of sprayed coatings in the direction of thermal stabilization of the polygonization substructure due to subsequent deformation of the obtained coatings was further developed. 
Findings and practical implications. The application of the research results obtained in this work provides an opportunity to expand the range of cheaper sprayed materials for coating with increased physical, mechanical and operational properties on heavily loaded parts of mechanical engineering, electrical products and parts of the military-industrial complex. 
Keywords: electric arc composite coatings, electric pulse action, heat treatment.