Abstract
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 (mu(R)) prior to reaching a low and stable steady-state COF (mu(s)). This study shows that incorporating titanium (Ti) atoms into the DLC structure would reduce the mu(R). 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), mu(s) 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 x 10(-5) mm(3)/Nm at 25 ?C to 0.71 x 10(-5) m(3)/Nm at 200 ?C. A typical DLC with 40 at.% H (H-DLC) tested at 200 ?C showed a low mu(s) of 0.08 and a wear rate of 1.11 x 10(-5) mm(3)/Nm. However, at 200 ?C, Ti-H-DLC showed a lower mu(R) of 0.16 compared to mu(R) = 0.78 of H-DLC, and the duration of the running-in period for Ti-H-DLC, t(R) = 3 revolutions, was shorter than H-DLC with t(R) 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.
NSTL
Elsevier