Investigation of tribological behaviour of a-C:H coatings for dry deep drawing of aluminium alloys

Lubricant-free sheet metal forming increases resource efficiency and contributes to environmental protection. However, the direct contact between work tool and workpiece leads to increasing friction and wear. One approach to reducing friction and wear in dry forming is the tool-sided application of carbon-based coatings. In this work, amorphous hydrogenated carbon (a-C:H) coatings were prepared by plasma-enhanced chemical vapour deposition (PECVD). The coating samples were deposited under different amounts and ratios of acetylene and argon gas atmospheres. The coating samples were characterised regarding their thickness and mechanical as well as chemical bond structures. The tribological behaviour against aluminium alloys was investigated under lubricant-free conditions with a ring-on-disc tribometer. Finally, one a-C:H coating variant with promising tribological performance against aluminium alloys was exemplarily tested in a flat strip drawing test, which models the tribological conditions in the flange area of a deep drawing process. With help of the test results, the friction and wear mechanisms during dry sliding in both closed and open tribological systems were discussed.