Funct. Mater. 2023; 30 (3): 363-370.
Features of the structure and properties of surface layers of babbitt coatings after boundary mode of friction
National Aviation University, 1 Liubomyra Guzara Ave., 03058 Kyiv, Ukraine
The microstructure and properties of the surface layers of the friction surface of the babbitt coating were studied after the boundary mode of friction. Its tribological characteristics were studied in a load-speed mode close to the operating conditions of plain bearings of gas-pumping units; cases of optimal antifriction behavior of the coating were revealed, when the coefficient of friction after short-term steam treatment decreased to 0.02. It was established that the mechanochemical processes in the friction contact zone of the babbitt-steel pair come to end with the formation of a submicrodisperse antifriction surface layer with an average grain size of 310 nm (for the B83 alloy). Near the surface, a fairly ordered fragmentation of the intergranular space with a fragment size of about 12 nm was observed. On the surface of the coating, the presence of an elementally compacted surface layer of a similar thickness was found. Highly dynamic processes of isomorphous replacement of the basic elements of the SnSbCu coating with carbon and oxygen, which are responsible for the appearance of a nanocomposite surface structure, are revealed. Oxygen stabilizes the content of copper in the surface grains, but, on the other hand, causes their depletion in antimony (an element of the strengthening phase). The intensification of mechanochemical oxidation significantly reduces the content of antimony in the surface friction layers of babbitt; this is obviously the main reason that babbitt coatings are not able to provide the necessary bearing capacity of bearings at elevated operating temperatures (above 100-120°C).
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