Fretting corrosion of tin-plated contacts: Evaluation of surface characteristics

The surface characteristics of the contact zone of tin-plated copper alloy contacts subjected to fretting motion for 8000, 16,800 and 48,000 cycles under unlubricated conditions are presented. The nature of the contact zone, at the verge of wearing out of the tin coating as well as upon the coating is completely worn out, is assessed using scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) analysis and X-ray dot mapping, and the influence of these changes on the contact resistance is correlated. The study reveals that under unlubricated conditions, fretting caused significant damage at the contact zone. Occurrence of adhesive wear failure is observed at early stages whereas at latter stages, delamination wear is the predominant mode of failure. As the fretting cycle increases, the concentration of copper increases whereas the concentration of tin decreases; oxygen concentration though not appreciable at the early stages, starts to build with increase in fretting cycles, attributing to the increase in contact resistance due to the formation of oxides of copper and tin at the contact zone.