Rolling contact fatigue performance of plasma sprayed coatings

Authors: Ahmed, R. and Hadfield, M.

Journal: Wear

Volume: 220

Issue: 1

Pages: 80-91

ISSN: 0043-1648

DOI: 10.1016/S0043-1648(98)00224-5

Abstract:

This experimental study describes the Rolling Contact Fatigue (RCF) performance and the failure mechanisms of plasma sprayed tungsten carbide cobalt (WC-15%Co) coatings. The advancements of plasma spray coatings 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 models the configuration of a deep groove rolling element ball bearing was used as an accelerated method to compare the rolling contact fatigue resistance of the test materials. RCF tests were conducted in conventional rolling element steel ball bearing (steel lower balls) and hybrid ceramic bearing (ceramic lower balls) contact configurations. Plasma sprayed coatings were deposited on a bearing steel (440-C) substrate at different thicknesses. The coated rolling element cones were ground and 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 torque 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 vibration signal. This enabled the experimental measurement of sliding between the coated cone and the driven balls. The failed rolling elements, coating debris and the lower planetary balls were analyzed for surface observations under the Scanning Electron Microscope (SEM), and Electro Probe Microscope Analysis (EPMA). The test results indicate that the coating performance was dependent upon the tribological conditions during the test. The failure modes were observed to be surface wear and the coating delamination.

Source: Scopus