High-temperature tribological behavior of Ti containing diamond-like carbon coatings with emphasis on running-in coefficient of friction

Diamond-like carbon (DLC) coatings show a low coefficient of friction (COF) and high wear resistance against aluminum at elevated temperatures, yet they exhibit a high running-in COF (μR) prior to reaching a low and stable steady-state COF (μs). This study shows that incorporating titanium (Ti) atoms into the DLC structure would reduce the μR. During pin-on-disk tests conducted on Ti incorporating hydrogenated-DLC (Ti-H-DLC) with 6.2 at.% Ti subjected to dry sliding against 319 Al (Al-6.5% Si), μs values decreased from 0.27 at 25 °C to 0.11 at 200 °C. The specific wear rate of Ti-H-DLC decreased from 2.44 × 10−5 mm3/Nm at 25 °C to 0.71 × 10−5 m3/Nm at 200 °C. A typical DLC with 40 at.% H (H-DLC) tested at 200 °C showed a low μs of 0.08 and a wear rate of 1.11 × 10−5 mm3/Nm. However, at 200 °C, Ti-H-DLC showed a lower μR of 0.16 compared to μR = 0.78 of H-DLC, and the duration of the running-in period for Ti-H-DLC, tR = 3 revolutions, was shorter than H-DLC with tR of 200 revolutions. Comparisons made with other DLCs, including, NH-DLC, W-DLC, ta-C, and Si-O-H-DLC, in addition to H-DLC, all tested using the same method, revealed that, in the temperature range of 100–250 °C, Ti-H-DLC showed a better running-in behavior making Ti-H-DLC a suitable tool coating for manufacturing processes where high-temperature running-in sliding friction is important, including warm forming and (single-point) turning of aluminum alloys. •High-temperature tribological behavior of Ti-H-DLC against 319 Al was studied.•Low running-in COF and short running-in duration were recorded at 100 and 200 °C.•Compared to other DLC coatings, the lowest μR and tR were obtained using Ti-H-DLC.•Ti-H-DLC tool coatings are useful for Al warm forming, machining operations ~200 °C.