Critical Thickness of the Hardening Coating Layer on the Working Surfaces of Injector Nozzle Parts

Motor vehicles and tractors operate in conditions of high dustiness. The main reason for the short service life of precision parts of fuel equipment (FE) is the abrasive wear of working surfaces. The innovative chemical vapor deposition (CVD) method of obtaining coatings by thermal decomposition of chromium hexacarbonyl with subsequent deposition of chromium carbides significantly increases the wear and corrosion resistance of the injector nozzle parts of diesel engines. To increase the service life of the sprayer, the authors propose to apply a hardening coating to both working surfaces of the parts, viz., the needle (steel R6M5) and the inner surface of the housing (steel 12Kh2N4А). In order to minimize costs in the manufacture of new precision parts, the authors determined the critical (minimum) coating thickness, ensuring its load-bearing capacity. They also obtained analytical relationships between the minimum required coating thickness depending on its microhardness and the size of quartz and corundum particles, as well as regression equations and response function graphs. It has been established that in order to ensure the bearing capacity of the hardening coating on the fuel injector nozzle parts of the diesel engine, its critical thickness should be not less than 3 micrometers at a microhardness of 18.9 GPa.