Some studies on life prediction of thermal sprayed coatings under rolling contact conditions

Design of engineering components is concerned with their strength and durability characteristics. While design for strength is influenced by the bulk material characteristics, the design for durability is dependant on the surface characteristics. Majority of the component failures are surface originated. Surface engineering could play a vital role in minimizing such failures. Thermal sprayed coatings, one of the versatile surface coating techniques, can be applied to components of machinery surfaces to avoid such failures. The present paper presents a methodology for contact stress evaluation of surface coated elements, adopting a layered structure approach, and thereby analytically predict their spalling life. Further data on cycles to single pit formation, and spalling of spray fused coatings obtained from experimental testing are presented for assessing the applicability of life prediction models to layered structures such as sprayed coatings. Experimental investigations were conducted on spray fused coatings using a twin disk RCF test setup. The surface and subsurface contact stress distribution have been obtained analytically by Smith-Liu equations along with first order model perturbation method (FOMP), to account for the variation of elastic modulus constants of the layered structure. Applying Lundberg-Palmgren and Tallian life prediction models, the spalling life of these coatings has been predicted analytically and compared with experimental life values.