Wear and wear transition mechanisms of ceramics

The combination of indentation, inclined-plane sliding, and wear tests provides useful and unique way to investigate ceramic wear and wear transition mechanisms. The experimental results show that wear mechanisms of ceramics are predominantly dependent on the tribological contact stresses. At low contact stress, the removal of material is controlled by plastic deformation induced microfracture on the asperity contact scale. Wear debris are produced when the plastic deformation exceeds the plasticity limit of the material, which is very limited for ceramics. As the tribological stress increases and reaches a critical point, various kinds of cracks (such as partial cone cracks, lateral/shallow cracks, and radial cracks etc.) are initiated. These cracks can propagate owing to subsequential contact or at higher contact stress. When these cracks intersect each other, chunks of material are detached from the bulk material and crushed by the subsequential tribological contact into fine particles and carried away from the contact region as wear debris. Wear transitions from deformation- to crack/fracture-controlled wear in ceramics can be attributed to the change of wear mechanisms during the sliding contact due to the tribological stress exceeding the critical microcrack stress or the fracture stress. With the inclined plane sliding test, a wide range of stresses can be applied progressively under one single sliding and the critical stress of the transition can be estimated. By using the results of repeated sliding test on an inclined plane, the wear and wear transition mechanisms have been demonstrated. Although ceramic wear mechanisms are dominated by fracture processes, tribochemical reaction products may be present to moderate the stress distribution by providing a reaction layer for wear protection.