The wear and lubrication performance of liquid-solid self-lubricated coatings

摘要

The use of solid lubricants (MoS_2, PTFE, graphite, etc.) embedded in coatings has been largely employed in different industries, especially in those applicationswhere liquid lubricants cannot be used. Although the use of liquid lubricants is desirable whenever it is possible, limited research has been addressed towards the development of self lubricated coatings containing liquid lubricants. One of the main reasons for this is due to the complexity of embedding lubricant reservoirs inside the coatings. This work focuses on the production of liquid lubricant filled capsules that will be used as reservoirs in thermally sprayed coatings. The capsules were used and injected in a conventional thermal spray process for obtaining the self lubricated coatings. The obtained coatings consist of embedded liquid lubricant filled capsules in a polymeric matrix. The lubricant contained in the capsules is released to the system whenever the coating is worn out, promoting the breakage of the capsules. Coatings obtained with different spraying parameters have been tested in this work. The characterization has been performed by optical microscopy and Scanning ElectronMicroscopy (SEM) techniques and the tribological properties (i.e.: self lubricating function and lubricant release) have been investigated by reciprocating ball-onplate tests using a stainless steel ball as counterpart. The wear tracks have been investigated using SEM. It was found that the coatings provided a good lubrication performance as long as the matrix material was not remelted after spraying using capsules with thin wall. For the non-remelted coatings, the coefficient of friction remained below 0.2 and the material loss varied depending on the normal load and on the spraying parameters. The coatings obtained with thick wall capsules resisted better the thermal input, but the lower amount of lubricant was insufficient to keep low friction under certain loading conditions.