Fretting of polyimide coatings Part I: Structure and moisture effects

Abstract Fretting wear of polyimide coatings sliding against a 52100 steel sphere as a function of humidity was measured. The coating life, defined as the duration for which the 52100 ball wore through the polyimide coating, shortened with increasing humidity. A hydrophobic fluorine was exploited to reduce the effect of moisture on the coating life. Microhardness tests showed that the hardness of the polyimides changes only after long time exposure to moisture suggesting that short time exposure to moisture as in the fretting test did not alter the bulk properties of the polyimides. For the wear mechanisms, the abrasive iron-rich debris generated from the 52100 ball in the polyimide-metal contact accelerated the fretting wear of the polyimides by two-body and three-body abrasion. Interpreting the debris as iron oxides did not fully account for the test results in argon, although such a model satisfactorily explained the results in air.