Metallurgical Analysis of Rainbow Rotor Coatings: Analysis of Fleet Blades

摘要

In a continuing effort to increase component lifespan and decrease overhaul cost, the US Navy has completed a 2nd phase of the Rainbow Rotor project. This project, initiated in the early 1990's, consists of three LM2500 main propulsion engine, high pressure turbines (HPT) built up with refurbished blade pairs protected by various coatings. This turbine was operated for over 7,000 hours on a Cruiser-class ship where it was subjected to a typical operating profile. Six coatings were examined ranging from differing chemical compositions to application processes. The coating compositions were of four types, CoCrAlHf, PtAl, Physical Vapor Deposition (PVD) Zirconia thermal barrier coating (TBC) with a PtAl bond coat and a silicon aluminide type coating. The BC-22 (CoCrAlHf) overlay coatings were applied by either a plasma spray process or an electroplating process. The PtAl coatings, supplied by two vendors, and the TBC were applied by standard commercial processes. The goal behind this study is to find a coating that has the best balance between cost and performance. With the already realized cost savings in using refurbished components to overhaul the gas turbine engine, the emphasis is now placed on delaying the deterioration of the reprocessed blade pairs. The following discussion covers all aspects of this completed phase.