Coatings for gas turbine materials and long term stability issues

This paper reviews protective coatings against the high temperature oxidation and corrosion of gas turbine components. Having briefly reviewed the development of gas turbine materials over the past 50 years, the need for corrosion protective coatings and their routes of application and chemistries are explored. The effects of varying coating chemistries and application methods is examined in the context of the major corrosive degradation mechanisms which operate in aircraft and industrial gas turbines. A case study relating to the interdiffusion of coatings and a typical third generation Ni-based alloy is presented which shows that this phenomenon may be of importance with respect to coating life. Finally the paper briefly investigates thermal barrier coatings and how their failure is attributable to the oxidation of the bond coats to which they are attached.