The effects of load and humidity on friction and life of polymeric coatings used to prevent fretting corrosion

Abstract

A statistical analysis was conducted to investigate the effect of applied load and relative humidity of the atmosphere on the durability and coefficient of friction of five polymer coatings used to protect against fretting corrosion. Chlorine and non-chlorine containing polymers were used in this research to see if the large humidity effect seen in a previous study with polyvinyl chloride is strictly a chlorine related phenomenon. The five polymers used were polyvinyl chloride, polyvinylidene chloride, polystyrene, and two siloxane modified polyimides.

Disks made of 1045 steel were coated with thin polymeric films and fretted against a 52100 steel ball. Three levels of load were used: 11.12, 22.25, and 44.5 N, and the two levels of relative humidity were less than 10% and between 45 and 55%. Amplitude of oscillation was 330 μm peak to peak, frequency of oscillation was 40 Hz, and the coating thickness was 25 μm.

Statistically significant variables and interactions are identified, and reasons for their significance are discussed. Increasing the humidity had no consistent effect on the ending coefficient of friction between the polymer film and the oscillating ball, increasing the load decreased the coefficient of friction, and either increasing the humidity or load decreased the life of the coating during fretting. The extent of this reduction in life depends on the polymer. The relative humidity of the environment affected the coating life of only one of the chlorine-containing polymers. Humidity was also shown to affect the coating life of two polymers that do not contain chlorine.