Two-layer laser clad coating as a replacement for chrome electroplating on forged steel

Chrome plating is one of many surface engineering techniques used for corrosion resistance, as well as a protective coating against surface damage in load bearing applications, with surface hardness in the region of 1000Hv. Laser cladding is an alternative hardfacing technique often chosen for corrosion resistance and for increasing the surface hardness of components, through thick clad coatings. The application of chrome plating and other similar surface engineering techniques for thick coatings can be inefficient and costly with practical process limitations. The objective of this case study was to investigate the feasibility of replacing the chrome plated layer of a rod mill pinion, made of forged steel, with a Nickel-based Tungsten-Carbide (Ni-WC) composite layer and an intermediate layer of Inconel 625. Mechanical properties were obtained using microhardness and nanoindentation techniques. Three-point bend tests were performed on test specimens from a pinion sample, in order to observe crack propagation resistance, a challenging task due to the curved geometry of the pinion sample and the difference in thickness between the existing and proposed coating layers. Crack development was captured, and plastic deformation was quantified with the use of Digital Image Correlation (DIC). In bending it was found that the bond between the composite coating, Inconel 625 and the steel substrate provided improved resistance to axial crack propagation, where the composite coating could withstand more than twice the bending tool displacement than the chrome electroplating.