Degradation of W-DLC Coatings in Rolling/Sliding Applications

W-DLC coatings have demonstrated the benefit to improve contact fatigue life in different applications. The understanding of coating degradation mechanism becomes important for coated component design. In this present study, FZG gear rig has been used to investigate coating wear. The testing procedure was designed to monitor coating wear with interruptions. Scanning Electron Microscope and surface profilometer were used to characterize coating wear. Cone-shaped micro particle pullouts were observed at low stress cycles. Fracture-based cohesive delamination is one form of coating wear associate with concentrated stresses. Another form of wear is characterized as polishing wear (or, sliding wear). The mechanism of polishing wear is complex and can be attributed to chemical or oxidation wear and abrasive wear. However, unlike fracture-based cohesive delamination, polishing wear results a smoother surface. The evolution of surface topography due to coating wear is demonstrated by profilometry measurements. Wear mode of W-DLC coating degradation is proposed as a combination of cohesive delamination and polishing wear.