Microstructure, mechanical and tribological properties of NbMoWTaAg refractory high entropy films with nano-layered self-organization

Although refractory high entropy films exhibit excellent strength and hardness, their high brittleness often leads to cracking upon frictional contact, resulting in wear resistance that falls short of expectations. This limitation severely restricts their application in industries such as aerospace. In order to address this issue, the development of high entropy composite films has emerged as a viable approach to mitigate friction and enhance reliability. In this paper, a series of (NbMoWTa)_1−xAg_x films were prepared by introducing nano phase Ag into the NbMoWTa system by magnetron sputtering co-deposition. Despite the soft second phase potentially deteriorating the mechanical performance of the composite films, our study demonstrates that the unique chemical nanolayering in the NbMoWTa/Ag can lead to a significant reduction in friction while maintain a high hardness. Compared with the monolithic NbMoWTa film, the (NbMoWTa)₇₅Ag₂₅ film exhibited a 54.3 % reduction in friction coefficient and an 81.6 % decrease in wear rate, demonstrating superior tribological behavior compared to most Ag-containing composite films. The present work provides an effective strategy and facile route, through self-assembling of layered phase, for developing high performance refractory high entropy alloy films.