A New Process to Produce Local Chromium Diffusion Coating

With increasing operating temperatures and more severe environments in today’s gas turbine engines, there is a need for a process to produce a localized chromium diffusion coating for protection against type II hot corrosion and stress corrosion cracking.  Conventional pack and vapor phase chromizing process have their limitations of applying such a local chrome coating.  Masking for these processes is costly and often unsatisfactory.  Therefore, pack and vapor phase chromizing process typically coat the entire part surface and then require undesirable post-coating treatment to remove excess chrome coating where no chrome coating is required.  This presentation will discuss a new slurry based process that produces a localized chromium diffusion coating on the selected regions of gas turbine components in a controlled and accurate manner.  No post-chromizing treatments such as machining or chemical treatment are required to remove excess chrome coating in comparison to conventional process.  The resultant coating chemistry and microstructure meet the OEMs’ specifications.  Other advantages of this new process include capability to coat large parts, and achieve uniform coating on parts having complex geometries such as shank and fir-tree root of turbine blades.  Examples of the local chrome coating that can be produced by this method will be presented.  In summary, the advantages of this local chromizing process make it attractive to coat the highly stressed regions of gas turbines for protection against type II hot corrosion attack and stress corrosion cracking attack.