Temperature-dependent contact phenomena of PVD- and CVD-deposited DLC films sliding on the thin aluminium foil

This paper reports on tribological properties of magnetron-sputtered WC-C and chemical-vapour deposited diamond-like carbon films coated onto hard-metal surfaces when sliding on aluminium foil (0.2 mm nominal thickness) at different temperatures. The study addresses the evolution of the coefficient of friction at the interfaces of the coated hard metal and the aluminium foil under dry-lubrication conditions, in a ball-on-disc configuration. The wear mechanisms of the aluminium foil and the damage produced on the coated surfaces due to the sticking of aluminium were evaluated as a function of the deposited coating and the temperature at their interfaces. Aluminium-transfer to WC-C coated hard-metal surfaces during the sliding operation seemed to be a non-continuous process, which appeared after a certain number of sliding cycles. Temperatures above 70ºC accelerated the transfer of aluminium to the WC-C tool surfaces. Chemical-vapour-deposited diamond-like carbon films hindered the transfer of aluminium to the hard metal even at temperatures of around 125ºC. At greater temperatures, an aluminium--aluminium tribo-surface is formed at the interface, which increases the wear rate of the foils and rapidly degrades the quality of coatings of the hard-metal surfaces.