Reducing operating clearance between the HP turbine and shroud is a means often used by engine manufacturers to improve the efficiency of new generation gas turbines. This, in turn, requires the development and use of clearance control coatings to minimize the effects of degradation and wear associated with rubbing. In this study, the authors assess two coating systems: VPS NiCoCrAlYTa coatings for blade tips and plasma-sprayed MCrAlY, a potential abradable coating. In order to understand the wear mechanisms of these systems, block-on-ring and fretting tests were conducted and the relationship between microstructure and wear was examined. The results were then compared to those of rub tests performed with real engine components.

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