Strain Compatible Oxidation and Corrosion Protection Coatings for Enhanced Thermo-Mechanical Durability of Turbine Airfoils

摘要

As critical components of advanced aircraft engines, turbine airfoils require coatings for the enhancement of oxidation, corrosion, and thermal capabilities. Airfoil coatings often constitute a significant fraction of the overall airfoil wall thickness and may therefore strongly influence the overall thermo-mechanical response of the turbine blade. However, to date, coatings have not been designed to enhance system performance, since the coating-substrate degradation mechanisms under relevant mechanical cycling conditions are not well understood and coating properties are often unknown. Damage that accumulates in turbine airfoils during service is driven by the superposition of centrifugal and vibratory stresses with airfoil surface compressive stresses that arise due to internal air cooling. Material degradation in this environment is poorly understood due the presence of the multiple material layers (one or more coatings, an interdiffusion zone and a superalloy substrate) that can crack, deform by creep, and oxidize simultaneously. Due to the complexity of the degradation process, improvements in airfoil durability are unlikely to be achieved without models of the degradation process that contain the essential materials and mechanics details. Thus the technical objectives of this research effort are threefold: (1) establish a fundamental, mechanistic understanding of the degradation processes that occur in superalloy components with coatings during thermo-mechanical cycling; (2) develop models for damage growth under cyclic conditions that can guide the development of strain compatible coating systems; and (3) transition models to Navy turbine manufacturers for their use in alloy coating design.