WEAR RESISTANCE OF ELECTROSPARK-DEPOSITED COATINGS IN DRY SLIDING FRICTION CONDITIONS

Abstract

The use of powder-cored wires as electrodes for electrospark deposition (ESD) of coatings onto quenched and low-tempered steel 45 was studied. The industrial PP-Np-PD80Kh20R3T powder-cored wire (PW) and powder-cored wire and a combined powder-cored wire with an MPG-7 graphite addition (PWG) were applied. The magnitudes of mechanical characteristics peculiar to the surface layer of an electrospark-deposited coating produced from powder-cored wires (hardness HV, friction coefficient m, elastic strain energy А_elast, and plastic strain energy А_plast) were established. Loading and kinetic indentation depth diagrams were plotted. The variation in penetration depth P_d and recovery R_d of the indenter in scratch testing of the ESD coatings produced from powder-cored wires were illustrated. Characteristic changes in the mechanical characteristics at a preset indenter penetration depth and the microstructure of the scratch-tested ESD powder-cored coatings were examined. The wear rate of the ESD coatings deposited with PW and PWG electrodes was established as a function of specific loading, sliding speed, and testing time. The variation in roughness of the friction surfaces and temperatures in the contact area in dry sliding friction conditions was studied. The PWG coating showed 24% higher hardness than the PW coating did and 10% lower friction coefficient determined by indentation. The roughness of the PWG coating increased by 10% when loading changed from 3 to 7 MPa. The PWG coating (pin-on-disk friction test) had 2.5 times higher wear resistance than the PW coating did, and the disk (counterface) had 28% lower wear. A slight increase in temperature in the tribological contact area was not found to soften the coating or substrate (quenched and low-tempered steel 45) but promoted regeneration of the protective oxidized layer and favorably influenced the friction process. Both materials produced from powder-cored wires (PW and PWG) exhibited normal mechanochemical wear in experimental conditions. The high wear resistance of the ESD coatings produced from powder-cored wires in dry friction conditions indicated that they would be beneficial for strengthening and improving the life of various machine parts and mechanisms in industrial mechanical engineering.