Low Friction Properties of ta-C:Ta Coating in Drilling of CFRP

In the aerospace industry, the increasing use of robot-assisted machining has led to a growing demand for drills with low cutting resistance.In this study, we investigated the cutting performance of tantalum-containing tetrahedral amorphous carbon (ta-C:Ta) coatings, which have been reported to exhibit lower friction coefficients than conventional ta-C under atmospheric friction tests.ta-C:Ta coatings with different Ta contents were deposited using an ion beam assisted filtered arc deposition (IBA-FAD) system by varying the Ta sputtering current.Their properties were characterized by nanoindentation, Raman spectroscopy, XPS, and wettability measurements.The results revealed a trade-off relationship between Ta content and both hardness and the I D /I G ratio.In addition, increasing Ta content promoted the formation of a Ta oxide surface layer, resulting in reduced surface free energy.Drilling tests on aerospace-grade PAN-based thermoset CFRP showed that thrust force after five holes decreased with increasing Ta content, with ta-C:Ta8.0exhibiting the lowest thrust force.However, ta-C:Ta8.0also showed the largest flank wear width among the deposited coatings, indicating inferior wear resistance.In contrast, ta-C:Ta3.5achieved reduced thrust force while maintaining wear resistance comparable to that of conventional ta-C.These findings suggest that a Ta content of approximately 3.5% is optimal for balancing low friction and wear resistance.