Microstructure and properties of Al and Al-Cr coatings on nickel-based superalloy GH625 by a thermal diffusion process

Abstract

Aluminide coating has been known as one of the best surface engineering approaches to combat high temperature corrosion in nickel-based superalloy. In this paper, A chromium-modified aluminide coating was prepared on the GH625 by the neutral salt bath method. The microstructure and properties of the modified coating was studied and compared with simple-aluminized coating by scanning electron microscope, x-ray diffraction techniques, depth elemental profiling analysis, microhardness and interface bonding force test. Surface SEM and EDS analysis show that the Al-Cr coating contains more Cr element, finer microstructure and fewer oxide inclusions. Surface XRD analysis shows that the phase structure of Al-Cr coating is different and the α-Cr phase has replaced Ni3Al and Al4CrNi15 phases in the Al coating. Cross section SEM and line scan analysis show that the microstructure of Al-Cr coating is more compact and the element distribution is more uniform than the Al coating. In addition, there is a significantly wider interface zone in the Al-Cr coating than that of Al coating. In the interface zone, there is an obvious Cr-rich area and a wider elemental diffusion area toward the substrate. As the result, the Al-Cr coating has higher microhardness and the interfacial bonding force between the coating and the substrate.