ROLLING-CONTACT FATIGUE PERFORMANCE OF PLASMA-SPRAYED COATINGS

This experimental study describes the Rolling Contact Fatigue (RCF) pe rformance and the failure mechanisms of plasma sprayed tungsten carbid e cobalt (WC-15%Co) coatings. The advancements of plasma spray coating s due to higher velocity and temperature of the impacting lamella call for investigations into new applications. One possible application is the rolling element bearing. A modified four ball machine which model s the configuration of a deep groove rolling element ball bearing was used as an accelerated method to compare the rolling contact fatigue r esistance of the test materials. RCF tests were conducted in conventio nal rolling element steel ball bearing (steel lower balls) and hybrid ceramic bearing (ceramic lower balls) contact configurations. Plasma s prayed coatings were deposited on a bearing steel (440-C) substrate at different thicknesses. The coated rolling element cones were ground a nd polished to achieve a good surface finish on the rolling elements. RCF tests were conducted under the various tribological conditions of contact stress, lubricant and test configurations. The frictional torq ue in the cup assembly was measured during the RCF tests with the aid of a force transducer. The speed of the planetary balls was monitored using an accelerometer and fast fourier transformation of the vibratio n signal. This enabled the experimental measurement of sliding between the coated cone and the driven balls. The failed rolling elements, co ating debris and the lower planetary balls were analyzed for surface o bservations under the Scanning Electron Microscope (SEM), and Electro Probe Microscope Analysis (EPMA). The test results indicate that the c oating performance was dependent upon the tribological conditions duri ng the test. The failure modes were observed to be surface wear and th e coating delamination. (C) 1998 Elsevier Science S.A. All rights rese rved.