An investigation into the performance of plasma and laser coatings under rolling contact.

Abstract

Rolling contact is experienced by a large number of components in mechanical designs. Examples include roller bearings and ink distribution rollers in the printing industry. Rolling contact results in surface wear. It is however possible to reduce rolling contact wear rates and surface fatigue by performing a surface modification such as powdered metal coating [35]. Powder coating methods such as Laser cladding and Plasma coating are two application processes that are completely different in method and therefore create different coating microstructures and bonding mechanisms between the coating and substrate. The aim of the research was to investigate the comparative rolling contact performance of two coating processes and two separate metal powder compositions. The coatings were applied to British standard En 9 steel test specimens. En 9 was selected due to its popular use in the manufacture of shafts, cylinders and rollers. Under rolling contact, material is removed from the surface as a result of wear and surface fatigue. Through testing and evaluation, the performance of the coating application processes were evaluated relative to one another and relative to the uncoated steel under rolling contact. The performance of the coating compositions were also evaluated against one another for a given coating application process. Results used to determine the performance of the coatings and coating processes were, the number of cycles to failure and the wear rates of the coated surface. Microstructure pictures of the coated surface were taken prior to testing and following testing. The pictures were used to qualitatively determine the effects of the rolling contact on the surfaces. Through the study of rolling contact, an explanation of the stresses induced in the contact area and the position of the maximum values were determined. The boundaries for the deformation regimes were identified through the understanding of the position of first yield and the shakedown limit under rolling contact. The theories of rolling contact fatigue are covered briefly as part of a better understanding of the failure mechanism however the experimentation is largely comparative based.