For moving parts operating at elevated temperatures, the suitable protective coatings were required to maintain their high-temperature tribological properties. Diamond-like carbon (DLC) films had attracted much attention as a candidates for these demanding applications, but poor high-temperature lubrication and wear resistance limited their further application. Boron doping is considered as a feasible method to improve high-temperature properties of DLC films. However, the effect of B doping on high-temperature tribological behavior of B-DLC films and its mechanism remain unclear. Here, B doped DLC films with various B contents were prepared using a superimposed high-power impulse magnetron sputtering and direct current magnetron sputtering (HiPIMS-DCMS) deposition system. The B content in the films was controlled by varying the number of boron carbide (B₄C) pellets in the graphite-B₄C mosaic target. The effect of B doping content on the microstructure and mechanical properties of B-DLC films was analyzed. In addition, the effect of B content on the tribological properties of B-DLC films at temperatures ranging from 25 ℃ to 550 ℃ was investigated to verify their potential use as high-temperature lubricating films. The results revealed that B was successfully incorporated into DLC matrix, and the B content in the films ranged from 0 to 6.80 at.%. The structure of B-DLC films was obviously dense with the increase of B doping content. The surface morphology of the films changed from relatively rough to smooth, and the value of surface roughness was as low as 1.29 nm. Appropriate doping of B enhanced the hardness and adhesion strength of the films and reduced the residual stress of the films. Meanwhile, the friction test results found that appropriate doping of B significantly improved the high-temperature tribological properties of the films. Moreover, B-DLC film with 4.57 at.% B exhibited ultralow friction coefficient of about 0.04 at 500 ℃. The excellent tribological properties were mainly attributed to the enhanced mechanical properties and friction-induced formation of graphitized carbon and boric oxide transfer layer on the wear track under specific temperature condition in air. These results showed that B-DLC films have great application potential under extreme thermal conditions.
 

B-DLC composite film, high-power impulse magnetron sputtering, high-temperature, friction and wear