Investigation of lubricated rolling sliding behaviour of WC/C, WC/C-CrN, DLC based coatings and plasma nitriding of steel for possible use in worm gearing

The aim is to find alternative solutions to the couple bronze-quenched and tempered steel, recognised as standard solution for worm gearing. A steel-steel coupling was considered, providing different surface modifications (i.e. plasma nitriding, WC/C, WC-CrN, DLC coatings) in order to enhance the lubricated wear behaviour of the tribo-pair. The severe working condition of worm gearing applications, i.e. high sliding to rolling ratio, lubricant temperature and radial load have been reproduced in laboratory tests, which were conducted up to a very long sliding distance (about 1.6-1.8.106 m). During the tests periodic inspection were carried out to evaluate the progressive weight loss and to observe the surface modifications. At the end of the test the wear curves have been determined by correlating the weight loss with the sliding distance and the surface has been examined by optical microscopy to determine whether wear damage occurred. For all materials conditions very limited surface modifications and noticeable performance improvements with respect to the reference bronze-steel coupling was observed, thus suggesting their use as promising alternative solutions in worm gearing applications.