In-situ formation of self-lubricating 2D layered tribo-films in TiVNbAlx-WC medium-entropy composites during sliding

Critical applications in aerospace, nuclear, and high-temperature industrial sectors demand metal-matrix self-lubricating materials that maintain stable tribological performance under extreme conditions. However, conventional solid lubricants suffer from inherent low strength and thermal instability. Here this work demonstrates a new type of friction-induced chemical transformation in TiVNbAl_x-WC (x = 0, 0.2) composites that creates adaptive lubrication through in-situ formation of high-entropy MAX phases and their delamination into self-organizing 2D layered tribo-films during sliding at 600 °C. WC particles undergo thermal decomposition at 600 °C, releasing carbon atoms that react with the Ti-V-Nb matrix to nucleate MAX phases. Sliding-induced stress gradients promote mechanochemical delamination, transforming bulk MAX phases into 2D layered structures. The resulting 2D tribo-films maintain friction coefficients of 0.38 at 600 °C. This approach demonstrates how compositional engineering can harness extreme tribological conditions to generate beneficial surface chemistry, transforming operational limitations into performance enablers.