High-temperature self-lubricating properties of single-phase high-entropy carbides under a vacuum environment

It is an enormous challenge to develop single-phase ceramics with satisfactory self-lubricity because of the strong chemical bonding and difficult to shearing. In this study, (Hf0.2X0.2Nb0.2Ta0.2Ti0.2)C (X is Zr, W, and V, respectively) single-phase high-entropy ceramics can in situ formed tribo-film on the contact region during sliding process to achieve an excellent self-lubricating property. The friction coefficient is as low as 0.34 at 400 degrees C. This originates from the carbon-rich tribo-films which are generated under the effect of high-temperature tribo-induced. With the test temperature increasing, the wear mechanism changes from abrasive wear to oxidative wear. For the 900 degrees C, the tribo-oxidative film limits the direct contact between tribo-couple and enhances the tribological performances. Moreover, the compositions of the tribo-films also have an important effect on the tribological behaviors. This novel design concept-using own constituent elements to generate a lubricating tribo-film will provide a new strategy for the study of the single-phase self-lubricating ceramics.