Advanced coating development for industrial/utility gas turbine engines

Laboratory hot corrosion rig tests were used to identify new superalloy overlay coatings which are more resistant to hot corrosion than current CoCrAlY (Co 20Cr12Al0.5Y) or NiCoCrAlY (Ni20Co20Cr12Al0.5Y) coatings. These resistant coatings consist of two layers, an inner layer of CoCrAlY or NiCo CrAlY and an outer layer of MCrAlY containing 20–35 wt.% Si. Procedures are described in which the outer layer is developed on the surface of conventional CoCrAlY or NiCoCrAlY coatings using electron beam physical vapor deposition techniques. The combustor rig tests used to evaluate these coatings are discussed in terms of their relevance to industrial or utility turbine hot corrosion.