Wear mechanisms of Co-Cr sputter deposited magnetic tapes in helical scan video tape recorders

The wear mechanisms of Co-Cr sputter-deposited tapes for perpendicular magnetic recording by rotary video heads in the still mode of video tape recorders were investigated by using two kinds of experimental apparatus. One is a rotary-head-type friction tester in which the surface of the rotating head can be observed continuously by a microscope with a stroboscope synchronized with the head rotation; the other is a scratch tester in which the scratched surface of a tape specimen can be observed in situ through the transparent hemispheric slider. It was found that the wear debris of the Co-Cr layer transfers onto the head surface, forms the asperities on the head, and scars the tape surface, with the increasing amount of head tracing. A carbon protective layer can prevent the Co-Cr layer from transferring onto the head and being subsequently scarred. However, the carbon protective layer may be peeled by the rotating head when the frictional force increases up to the interfacial shearing strength between the carbon layer and the Co-Cr layer