Effect of humidity on wear of M-50 steel with a branched perfluoropolyalkylether lubricant

Humidity is an uncontrolled variable in many tribology tests. This report s hows that changes in relative humidity can affect wear for all perfluoropol yalkylethers regardless of their molecular structure. Using a Cameron-Plint tribometer under controlled environmental conditions, wear of M-50 steel w ith a Krytox (a branched perfluoropolyalkylether) lubricant was studied und er boundary lubrication conditions at 150(degrees)C in air with relative hu midity ranging from 1 to 95%. Both wear and friction decreased sharply as h umidity was increased from 1 to 20%, then were constant as the humidity was increased to 95%. Thus, wear is highly dependent on humidity when relative humidity is less than 20%. The similar effect of humidity on wear previous ly observed for Fomblin Z, a linear perfluoropolyalkylether containing difl uoroacetal groups, and Demnum S, a linear perfluoropolyalkylether which doe s not contain difluoroacetal groups, indicates that this may be a general p roperty of all commercially available perfluoropolyalkylethers, branched as well as linear ones.