Laser Remelting for Enhancing Tribological Performances of a Ductile Iron

With the aim to improve the tribological behaviour of a high performance component made of a ferritic ductile cast iron (GJS400-12), a laser surface modification treatment by a solid-state laser beam is proposed. The induced microstructural modifications have been investigated in a previous experimental work by means of experimental tests in various process conditions. It was thus possible to verify that the achieved hardness profile is a function of the energy density delivered towards the surface and that the process shows a saturation phenomenon when melting occurs. Depending on the available process power and the interaction time for microstructural modification, the higher energy density determines the deeper transformation: initially related to the diffusion mechanisms in the solid matter and then due to the melting of the outer layers. In the present study, the tribological behaviour of the laser remelted ductile cast iron was compared to the base material in order to evaluate the performance enhancement. The highest achieved value of the surface hardness was selected for the tests. The tribological behaviour has been investigated by means of dry sliding tests carried out on a flat-on-cylinder tribometer (block-on-ring contact geometry). Flat sliders consisted of the untreated and laser surface treated ductile cast iron, while the rotating cylinder was a carburised UNI-EN 16MnCr5 steel. The tests allowed measuring and comparing the coefficient of friction and the volume of loss for the untreated and laser modified material. Laser surface treatment led to a significant increase in the wear resistance of the ferritic ductile cast iron, due to the enhanced surface hardness; the coefficient of friction however increased, due an increase of both the adhesive and abrasive component.