Tribology of diamond-like carbon coated VCR head drums

Friction and wear behaviours between video cassette recorder (VCR) head drum and tape were investigated by using a home made tribometer. Friction coefficients of uncoated and diamond-like carbon (DLC) coated head drums of Al alloy were compared before and after a wear test. Diamond-like carbon films were deposited by high frequency plasma enhanced chemical vapour deposition method. The friction coefficients were measured in the range of sliding speed from 0.16 to 4.9 m s(-1). The friction coefficients of DLC coated head drums have 14% to 30% lower than those of the uncoated head drums at low sliding speed (0.16 m s(-1)). At high sliding speed beyond 3.2 m s(-1), both friction coefficients have similar low values less than 0.1 because air gap is formed between the head drum and the tape. However, the friction coefficients of uncoated head drum significantly increase after the wear test. Furthermore, the friction coefficients become essentially same regardless of the sliding speed. In contrast, those of DLC coated VCR head drums have almost same values as those before the wear test. These contrasting behaviours were discussed in terms of surface damages of uncoated head drum surface mainly due to the embedded Fe oxide particles which is transferred from the test tape. It is further observed that the damage to the test tape is much reduced when using DLC coated head drums. These results show that the DLC coating on a VCR head drum can protect both the head drum surface and the VCR tape.