Radial fretting fatigue damage of surface coatings

Radial fretting tests with a 52100 steel ball-on-flat contact have been car ried out under different normal loads. TiN,MoS2 and TiN + MoS2 coatings on a 1045 steel flat were examined. The normal loads amplitude used were 200, 400 and 800 N at speeds of 12 and 1.2 mm/min. Dynamic analysis in combinati on with microscopic examinations by SEM and EDX have been performed. It was observed that the vertical stiffness increased with the increase of loadin g speed and number of cycles. The metallographic examinations showed that l ittle damage was observed for the MoS2 coating, which exhibited excellent r adial fretting fatigue resistance. For the TiN coating, micro-cracks appear ed at the lower load while delamination occurred at the higher load. For th e TiN + MoS2 composite coating, the vertical stiffness increased but accomp anied by some micro-cracks. As a result of the study, the radial fretting t est is proposed as one possible new method to evaluate coating life. (C) 20 01 Elsevier Science B.V. All rights reserved.