Design and Characterization of Self Lubricating Refractory High Entropy\n Alloy Based Multilayered Films

Abstract

Refractory high entropy alloys (RHEA) have been proven to have excellent\nmechanical properties with a potential use as protective thin films. However,\nthe combination of high hardness with low friction and wear is a major\nchallenge in the design of self lubricating RHEA films. In this study, we show\nthat designing of NbMoWTa/Ag multilayered films give a remarkable reduction in\nfriction and at same time maintain high hardness. Interestingly, it's found\nthat the bcc superlattice dominates in both layers and the interfaces are\nhighly coherent when the individual layer thickness h is reduced below 10 nm.\nThe film properties are then strongly dependent on h ranging from 100 to 2.5\nnm, and the most promising properties are obtained when the interface structure\ntransforms from incoherent to coherent ones. Specially, the multilayer with h =\n2.5 nm exhibits superior tribological performance over monolithic NbMoWTa, due\nto the significant coherent strengthening along with the self-lubricating\nability in the multilayer. This tailored phase transition and coherent\nstructure between matrix and lubrication phases can also provide an optimal\nwear rate-coefficient of friction (COF) combination, which is higher than most\nof the Ag containing self lubricating films. The current work might open a new\nroute towards the development of innovative self lubricating RHEA films with\nexcellent tribological properties in general.\n