Mutually enhanced mechanical and tribological properties in magnetron sputtered Mo2N/Ag-SiNx self-lubricating multilayered films via epitaxial growth design

: Achieving simultaneous enhancement of both mechanical and self-lubricating properties by incorporating soft lubricants into nitride films has been a longstanding challenge in the development of solid lubricant materials. This paper introduced a novel approach to overcome this challenge by developing coherent-structured Mo 2 N/Ag-SiN x multilayered films using radio frequency (RF) magnetron sputtering. The multilayer films were designed with a fixed modulation period of 30 nm, while the modulation ratio (γ) was varied from 1:9 to 1:1. The Mo 2 N layers exhibited a single fcc-Mo 2 N phase, while the Ag-SiN x layers formed a dual-phase structure comprising fcc-Ag nanoparticles embedded in an amorphous SiN x matrix. At a modulation ratio of 1:9, the Ag-SiN x layer epitaxially grew on the Mo 2 N template, resulting in a coherent structure. This coherent structure significantly enhanced both the hardness and elastic modulus, reaching approximately 36 GPa and 230 GPa, respectively. The improved wear resistance at room temperature can be attributed to the coherent strengthening effect, which not only elevated the film’s hardness but also eliminated sharp interfaces between modulation layers, thereby reducing crack initiation sites. In temperature-cycling tribo-testing from room temperature to 600 °C, the film with a γ of 1:9 maintained a stable coefficient of friction around 0.2, except during the initial room temperature, where it was 0.4. The wear rate could not be accurately calculated due to the adhered tribolayer on the top of the wear track following the initial tribo-test at 600 °C. The excellent tribological properties across temperature cycles were attributed to the synergistic lubricant characteristics of both layers and the formation of self-lubricating tribo-phases. The optimized Mo 2 N/Ag-SiN x multilayered films provide an effective balance of lubrication and mechanical stability under extreme conditions, making them highly promising for high-performance engineering applications.