Abstract
Problem. Improving the reliability and durability of piston rings operating in conditions of friction and wear, requires the improvement of existing and the development of new technologies. Existing hardening technologies are imperfect, as they can lead to warping of the surface of products, changes in the microgeometry of parts, the appearance of stresses, and environmental problems. The currently applied electrolytic chrome plating does not satisfy the increasing requirements for the properties of piston rings made of high-strength cast iron. Instead, proposed steel-molybdenum coating applied by the method of two-wire metallization. The technological process of applying steel-molybdenum coating on piston rings includes the following steps: pre-cleaning, shot blasting, direct spraying. Molybdenum and steel wire was fed at a certain speed, molybdenum wire was connected to the positive pole of the power source, steel - to the negative. The study of the microstructure of the obtained coating showed that it has a layered character typical for gas-thermal coatings with pores evenly spaced in thickness (up to 12%). The porosity of the coating provides increased oil absorption of the rings, which has a positive effect on the process of burn-in of the working pair of liner - piston ring and on the operation of piston rings during operation. After etching, the microstructure is a combination of molybdenum and steel. In addition to the two main phases in the coating, other structural components are observed, which are products of the interaction of steel and molybdenum wires with oxygen and nitrogen of air, as well as products of interaction between each other of molybdenum and steel in the process of plasma spraying. The results obtained in the study of antifriction properties indicate a higher durability and better antifriction characteristics of piston rings with steel-molybdenum coating in comparison with electrolytic chromic. Steel-molybdenum coating at least wears out the mating material and has a lower coefficient of friction. High performance steel-molybdenum coating can be explained by the specific properties of molybdenum oxides, which can have an additional lubricating effect, acting as a solid lubricant. In addition, the high melting point of molybdenum contributes to a lower tendency to setting of the mating materials.
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