Breakage of thermal sprayed coating under lubrication

Abstract

Thermal sprayed coatings are applied to lubricated sliding surfaces of engine components recently.
Small size peelings were observed on the ceramic coated test pieces tested with a pin on disk wear tester. The mechanism of peelings was investigated.
A test in which a ball was rolled on the coated surface was carried out. The test was considered to be appropriate for evaluating the peeling property of coatings for the correlation to wear test results. The rolling test results show that the peeling was not affected by the change of temperature but was strongly affected by the existence of lubricating oil. The same tendency was also observed in a cyclic loading test. Cross sectional view of tested surface shows a Hertz crack connected to a horizontal crack. Peelings can be caused by the formation of these cracks. Crack propagation is accelerated by the existence of lubricating oil. It is considered that the oil enclosed in the crack is pressurized by load and it expands the crack.