Mechanical and tribological properties of protective and recovering coatings of the working chamfer of internal combustion engine valves

Over the past 7-10 years, there has been a steady increase in the cost of gasoline and gas fuel. This circumstance forces the enterprises operating automotive equipment to switch to the use of gas-powered fuel. (Research purpose) The research purpose is in creating a protective and recovering coating that can withstand the wear of the working chamfer of the valve caused by high operating temperatures, dry friction in the valve–seat interface, as well as high flow rates of exhaust gas. (Materials and methods) The article presents an analysis of a priori information, which resulted in the following powder compositions: Ni- ZrO2-SiC; Ni–B4C–BN–ZrO2; Ni–B4C–ZrO2–MgO; Ni-B4C. The samples were subjected to tests on the SMT 2070 friction machine under boundary friction conditions to determine the tribological parameters of coatings made of these materials. The parameters of the friction moment and the coefficient of friction were taken during the tests, depending on the applied load on the tribo-coupling. (Results and discussion) At the first stage of the research, the microhardness of the coatings was analyzed. Tribological studies were performed depending on the microhardness of the coatings. Along with the economic effect, there are negative factors that affect the performance of the valve-seat coupling: increased temperatures up to 750-800 degrees Celsius, the transition to dry friction, high exhaust rates of combustion products (over 1000 meters per second). The best value of the coefficient of friction obtained during the tests belongs to the composition Ni–ZrO2–SiC, which takes values below 0.1. (Conclusions) The use of standard and well-known methods of protecting the working chamfer of the valve in this case is ineffective, since it does not provide the required operating conditions. The article recommens the use of Ni-ZrO2-SiC as the material of the protective and restorative coating of the working chamfer of the valve.