Friction and wear behaviour of mosaic surfaces formed by laser line remelting of cast iron

Abstract

Friction-controlled hard surfaces have been produced by laser line remelting of globular cast iron introducing a linear network of white cast iron lines. These “mosaic” coatings offer interesting tribological behaviour. Dynamic friction and wear of these coatings has been investigated using a hardened steel ball on a reciprocating flat tribometer. The dynamic friction coefficient depended on the tribochemical film formation at the sliding interfaces. Low friction values were measured between the steel ball and globular cast iron lines associated with the adhesion and transfer mechanisms of graphite. The graphite contribution was still very low with the test conditions adopted. Higher friction values were recorded for white cast iron lines owing to the poorer graphite adhesion and transfer mechanisms. Friction tests running perpendicular to the alternating globular and white cast iron gave a nonlinear variation of friction coefficient with relative proportions of globular and white cast iron in the mosaic microstructure. Friction-related wear resistance was estimated by using multi-pass profilometric analysis of the friction traces and the recorded tangential force was used to calculate the energy per unit volume of removed material. Optimal behaviour, low friction coefficient and high friction-related wear resistance, was obtained for a 60% surface fraction of white cast iron. These promising results bode well for the future of mosaic coatings as localized treatments in the control of friction and wear.