Fiber laser surface remelting of a nickel-based superalloy by an integrated rectangular laser spot

In some specific industrial applications employing nickel-based superalloy components, a surface enhancement of product tribological properties is required. In this work, the effects of a Laser Surface Remelting on a nickel-based superalloy was investigated. An Ytterbium fiber laser, with maximum power of 4 kW, and a focusing segmented mirror, which produces an integrated laser beam (in a knife blade or rectangular spot) as well as a laser intensity homogenization, were used. Different values of laser power and scanning speed were tested. Remelted tracks, having a width of 8 mm, were characterized in terms of surface visual inspection, morphology, metallographic examination as well as longitudinal and transverse micro-hardness. Moreover, a comparison was performed between properties of the remelted material and the base alloy. The particular optical setup allowed the width of the molten tracks remained almost constant also varying the process parameters. The quality of the treated surface, for a given power, improved with increasing scanning speed, even if the depth of the molten area reduced. Micro-hardness increased of about 14% because of the formation of very fine columnar-dendritic grains, due to the rapid remelting and resolidification. Process efficiency was also evaluated by two different parameters: the analysis of both allowed to state that, keeping the laser power constant, the efficiency of the process increased almost linearly with the speed.