Transfer Film Formation

In polymer-metal sliding contacts, transfer films significantly effect friction and wear. Despite intensive research, little is known about transfer film formation in non-standard climates. Therefore, a device for performing transfer film luminance analysis (TLA) in such climates was designed, fabricated and assembled. Preliminary experiments on tribologically modified polyamide sliding dry against 100Cr6 at 40°C indicate that transfer film formation is significantly enhanced by higher humidity. At the same time, however, the observed coefficient of friction also increases with humidity. This initially contradicts the usual explanation that more water is absorbed on the metal surface at higher humidity which should reduce the coefficient of friction. Only the realization that high humidity also favors transfer film formation provides an explanation for the observation made, since the increased adhesion between transfer film and polymeric test specimen compared to metal/plastic friction is a known effect of the formation of polymer-based transfer films.

Increased humidity favors the formation of polymerbased transfer films which in turn explains the observed  increase in the coefficient of friction with increasing humidity due to adhesion.