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.
Materials and manufacturing of advanced industrial gas turbine components
Industrial gas turbines (IGTs) require materials serving 50 000 h at temperatures up to 1050°C under high loading in an aggressive environment. These requirements are different compared to the aircraft engines, which have typically higher peak temperature for a short time, but with cruise cycle temperature significantly lower than the base load temperature for IGT. Gas turbine material development and application is always a compromise between strength and stability, between oxidation and hot corrosion resistance, between coating protection and diffusion-induced degradation, between application of most advanced materials and manufacturing technologies and requirement for an extensive engine experience. This paper gives an overview of gas turbine materials selection, trends in high-temperature materials, environmental and temperature-protective coatings, and in some of manufacturing techniques for industrial gas turbine components.
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