Micro/nanoscale differential wear and corrosion of multiphase materials

Wear of multiphase materials at the micro/nanoscale is important in devices such as magnetic tape and disk drives, where the thin-film read-write heads are multiphase. Differential wear, which is caused by differences in wear resistance among the head's phases, causes thin-film poles to recede from the head's bearing surface; this phenomenon is called pole tip recession (PTR). It is a problem because it increases spacing between the poles and medium, resulting in lower write density.; Here, PTR in tape heads is studied to understand micro/nanoscale differential wear. Test results suggest that three-body abrasion, which leads to primarily plastic wear, is the operative wear mode. Most of the three-body abrasive particles originate from the tape surface; the alumina head-cleaning agents (HCAs) in the tape, which function as load bearing particles at the interface, are the primary abrasives. Some particles originate from the head substrate.; PTR can be reduced by: lowering tape tension, choosing a substrate that is harder than the tape's HCAs, choosing a pole material that is as close as possible to the hardness of the substrate, and lowering the thickness of the head's thin-film region to a value as low as possible. Material hardness matching, i.e. choosing the substrate and pole materials such that their hardness values are close to equal, will not reduce PTR if a substrate is chosen that is less hard than the HCAs. Covering the head with a diamond-like carbon (DLC) coating reduces PTR in the short term.; An analytical model that accounts for the observed wear is presented. The model shows that each of the following leads to higher differential wear: increasing the thickness of three-body particles, increasing tension, decreasing thin-film hardness, and increasing the thin-film wear coefficient. An increase in thin-film wear coefficient can be caused by an increase in thin-film thickness or an increase in the number of particles at the interface.; Battelle Class II and elevated temperature & humidity tests have been conducted to study corrosion of tapes and heads. The addition of DLC coatings increases the corrosion resistance of heads; the coating inhibits contact between environmental pollutants and the metal surfaces.