Effect of diamondlike carbon coating and surface topography on the performance of metal evaporated magnetic tapes

Abstract

In this study, metal evaporated (ME) tapes with and without diamondlike carbon (DLC) coating were tested for friction, wear, and magnetic performance. Performance of flat DLC ME tape is compared with two non-DEC ME tapes (one being flat and the other with waviness). By using a commercial VCR as a magnetometer and the Wallace equation, changes in the rms head output level were correlated to changes in head-to-tape spacing as tape wear occurred during play/rewind cycling tests. Interface stability and recording performance at a 0.6 /spl mu/m recording wavelength were measured to bit level resolution using a dropout counter. Some pause mode and environmental testing were also performed. Tribological performance and magnetic reliability of ME tape was affected by waviness of the ME tape surface as well as by the presence of a DLC coating. Waviness of one kind of non-DEC ME tape caused poor magnetic performance and localized wear of the tape surface, but loose wear debris could escape contact areas by settling into valleys on the tape surface. In the case of flat non-DLC ME tape, loose wear debris could not escape from contact areas leading to early failure. DLC coating prevented catastrophic abrasive wear and reduction in head-to-tape spacing or intimate contact during cycling tests, but could not significantly improve the durability of ME tape. DLC coating reduces asperity compliance as compared to non-DEC tapes. All ME tapes failed by lateral crack formation (cracks often propagated through coating defects) driven by longitudinal tape tension or flexing of the tape in the transport. In pause mode, DLC coating improved magnetic reliability and tribological performance by preventing the heads from contacting the metallic magnetic layer. Based on this study, a flat tape must be used for magnetic considerations and DLC coating is needed to prevent abrasive wear and intimate contact. Reducing the number of coating defects and optimization of the toughness of magnetic and DLC coatings are key parameters for future ME tapes. At fixed temperature, high relative humidity leads to severe tape instability and high dropout frequency. At high specific humidities, lower temperature leads to severe tape instability and high dropout frequency. Bearing ratio curves for the tapes determine the onset of high friction and tape instability at high humidities.