Galling-resistant Co-free hardfacings for light water reactors

Galling, or adhesive wear, is a phenomenon that occurs, for example, in the mating surfaces of valves. Galling-resistant materials such as Stellites using a Co-Cr matrix with a high fraction of carbide precipitates that provide hard, non-adhesive areal coverage. Unfortuantely, the wear debris activates in the reactor core, giving rise to an operator exposure challenge, moptivating the development of Co-free hardfacings. Understanding how these corrosion-resistant iron-based hardfacings behave is a characterisation challenge that takes galling beyond its traditional disciplinary home in Mechanical Engineering. With the proposed powder metallurgy routes, understanding the phase metallurgy is the first challenge, requiring X-ray diffraction and synergistic EDX - EBSD-based phase characterisation. Then understanding the galling behaviour and particularly the stress-induced transformations and corrosion scales requires further (S)TEM-based characterisation and potentially, surface chemistry on light elements such as through SIMS and/or atom probe tomography.