Jan Gerkema

Lead thin film lubrication

Abstract Lead thin film coatings were studied in high vacuum between 20 and 300 °C using a steel ball-on-disc test rig loaded with 2.5, 5 and 10 N. The coatings were sputtered and electroplated. Experimental results of sliding distances are given for single lead coatings, Pb M (M = Mo, Ta, W, Ag, Cu) double layers and lead films containing a small amount of silver, copper, platinum or molybdenum. For single lead coatings, we found sliding distances comparable with reported distances for ion-plated lead films. The introduction of a copper interlayer and the metal dopants copper, platinum and molybdenum substantially extended the sliding distance. To improve the sliding distance of lead coatings it is essential that 1. (1) the Pb-Pb binding gives the weakest bond, 2. (2) the lead and underlying layer are mutually insoluble and 3. (3) the underlying layer itself has a lubricating ability. The mechanism of the breakdown process of the lead coating is discussed in terms of adhesion at the interface occurring between contacting surfaces during the sliding process.