Laser remelting of plasma-sprayed coatings on nuclear valves

Three kinds of plasma sprayed coatings on nuclear valves of FRAMATOME, which are the cobalt-based Stellite, the nickel-based Eutroloy, and the iron-based Cenium, were remelted with a 5 kW CO 2 laser. The aim is to build-up a fine homogeneous metallurgical structure onto the hardface, with a uniform thickness and free of cracks in order to improve the wear and galling properties of the coatings. It was concluded from the experimental results that for plasma sprayed Stellite coating, satisfactory results can be obtained by carefully selecting the process parameters, preheating of the substrate is not needed; and for the Eutroloy coating, preheating of the substrate is necessary to get rid of cracking during laser remelting. Laser remelting is not an adequate process for Cerium coating because it is very difficult to avoid cracks on the remelted layer.