Synthesis of multilayer diamond-like carbon/SiC lubricating coating for the steel drill-bit based on magnetron sputtering

A lubricating coating was designed and deposited on tungsten steel-based drills using magnetron sputtering technology to enhance performance in drilling epoxy-glass fiber printed circuit boards. Friction tests on single-layer films indicated that the diamond-like carbon (DLC) layer exhibited a lower coefficient of friction (around 0.11 against steel) than the silicon carbide (SiC) layer, leading to its selection as the outermost layer of the coating. A multilayered structure comprising ten alternating DLC/SiC layers was employed to mitigate the continuous buildup of internal stress inherent in single-layer films. This hard/soft layer configuration also helped alleviate the significant hardness mismatch between the functional coating and the alloy substrate. Furthermore, the alternating structure promoted greater elastic deformation within the coating, which further reduced the friction coefficient to the range of 0.16–0.18 against the epoxy-glass fiber and enhanced the solid lubrication effect. Meanwhile, the nano-hardness of the coated steel increased to 11.0 GPa from 4.8 GPa for the uncoated steel. Prior to the deposition of the functional layers, a titanium layer was predeposited onto the drill surface. This Ti layer formed a high-strength bond with the subsequent SiC interlayer, effectively eliminating the interface mismatch between the functional coating and the alloy substrate. This approach successfully resolved the issue of poor coating adhesion on the alloy surface. Compared with uncoated drills, the coated tungsten steel-based drills demonstrated significantly improved drilling performance on epoxy-glass fiber boards.