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 t ransition mechanisms. The experimental results show that wear mechanis ms of ceramics are predominantly dependent on the tribological contact stresses. At low contact stress, the removal of material is controlle d 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 cerami cs. 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 propa gate owing to subsequential contact or at higher contact stress. When these cracks intersect each other, chunks of material are detached fro m the bulk material and crushed by the subsequential tribological cont act into fine particles and carried away from the contact region as we ar debris. Wear transitions from deformation- to crack/fracture-contro lled wear in ceramics can be attributed to the change of wear mechanis ms during the sliding contact due to the tribological stress exceeding the critical microcrack stress or the fracture stress. With the incli ned plane sliding test, a wide range of stresses can be applied progre ssively under one single sliding and the critical stress of the transi tion can be estimated. By using the results of repeated sliding test o n an inclined plane, the wear and wear transition mechanisms have been demonstrated. Although ceramic wear mechanisms are dominated by fract ure processes, tribochemical reaction products may be present to moder ate the stress distribution by providing a reaction layer for wear pro tection.