A FRACTURE MODEL FOR WEAR MECHANISM IN PLASMA SPRAYED CERAMIC COATING MATERIALS

Wear resistant WC and Cr2O3 coatings were applied on to stainless steel ring surfaces by the plasma spray technique. Wear tests were conducted employing conforming and non-conforming block-on-ring arrangements in which coated rings slid against 45# mild steel or stainless steel. The worn surfaces and cross-section surfaces of the coatings and steel were examined using scanning electron microscopy. The wear rates of the coatings were measured and the results showed that the wear rates were related to the normal load by an exponent of 2/3. The mechanisms of the coating material removal during wear were examined The hard particles fractured from the coating surface were trapped in the interfacial layer on the steel surface. These impregnated particles acted like moving indenters, and caused median fractures on the coating surfaces as well as fractures between layers in the coatings (lateral fracture). The extension of the median crack was found to be the controlling factor. A model based on the median fracture extension mechanism was set up and it was found that the model agreed well with the experimental results. The difference of wear mechanisms between ceramic coating materials and bulk ceramics was also discussed.