The desire to improve the performance and efficiency of gas turbine engines has led to higher operating temperatures in the turbine sections of the engine. Present materials and materials under development for hot section turbine blades and vanes are not inherently resistant to hot corrosion, and therefore require protective coatings. In the past two decades this has led to increased use of thermally sprayed MCrAlY coatings, both as stand-alone overlay and as a bond coat for thermal barrier coatings.
This paper reviews the issues involved in thermally sprayed MCrAlY and TB coatings onto hot section blades and vanes of industrial gas turbines. The generation of a specification for coating acceptance and its practical implications are discussed. The issues in applying such coatings will be discussed, along with references to manufacturing issues on the shop floor. The difficulties inherent in applying a line-of-sight coating to complex geometric shapes will be discussed, with particular reference to robotics spraying. The utility of using a design-of-experiment approach to satisfy the user will be reviewed. The testing, evaluation, and performance characteristics of typical coatings are discussed.