Application of transient current measurements: evidence for galvanic corrosive wear of aluminum by a polyperfluoroether lubricant

Transient currents serve as a sensitive probe of electrical activity during a tribology experiment. Using this tool, we have found evidence for electrochemically-enhanced corrosion and galvanic corrosive wear of Al-6061 alloy in the presence of a perfluoropolyether (PFPE) lubricant, Fomblin Z-DOL. Galvanic current and potential measurements were carried out in three experimental configurations: (1) an Al stylus was translated across a Z-DOL-coated Al substrate in a typical wear geometry, (2) an Al electrode was brought down perpendicularly onto an identical, Z-DOL-coated Al electrode, and (3) in a simple electrolytic cell. All configurations yielded readily measurable currents with corresponding potential differences of similar to 300 mV. Corrosion during long-term Z-DOL exposure in galvanic cells was confirmed by the detection of significant Al concentrations in the oil. Analysis of oil employed in non-galvanic cells (same geometry, but no external electrical connection) showed essentially background Al concentrations. Scanning force microscopy (SFM) of Al surfaces exposed to Z-DOL in galvanic cells were actually smoother than as-polished surfaces due to an electropolishing effect. The consequences of galvanic corrosion regarding lubricant lifetime and wear in applications of PFPE lubricants, including magnetic disks, are discussed. (C) 1998 Elsevier Science S.A.