Design and Environmental Factors Contributing to the Failure of Thermal Barrier Coating Systems
Dr. Matthew D. Weeks
Naval Air Systems Command
China Lake, CA
Gas turbine engines are an indispensable component of 21st century air and sea propulsion systems and are also a critical component in large-scale electricity generation. The hot-section components of these engines are protected by a complex ceramic and metal multi-layer coating called a thermal barrier coating (TBC) system. The failure of TBC systems occurs as a result of both thermo-chemical and thermo-mechanical degradation. Metal constituents in a TBC system are subject to creep, corrosion, and oxidation while the ceramic components are subject to residual processing stresses, high compressive oxide growth stresses, phase changes, microstructural evolution, and foreign object damage. As a result of this perilous environment, there is a constant driver to better understand and predict coating failure. Predicting coting failure accurately is particularly difficult in air-plasma sprayed (APS) TBC systems. In this case, there is an additional and significant variable that comes into play: coating-substrate interfacial morphology. The morphology of the metal-ceramic interface is known to play a key role in the generation of compressive and tensile stresses that eventually cause coating failure in typical engine environments. Unfortunately, the optimum interfacial morphology in these systems is neither perfectly smooth nor infinitely tortuous. Experimental evidence and field experience have shown that some degree of interfacial tortuosity is generally beneficial to coating lifetime, but, for the past 40 years engineers have struggled to define “optimum”. This study is focused on finding a functional correlation between BC topology and coating system lifetime in APS TBC systems. This talk will address the progress that has been made toward the establishment of this functional correlation.
Dr. Matthew Weeks is a Navy research scientist at the Naval Air Warfare Center Weapons Division in China Lake, CA and is a recent graduate of the ChEMS department at the University of California, Irvine. Weeks graduated from UCI with a Ph.D. in Materials Science in September of 2011. He received his B.S. in Chemistry with minors in Physics and Mathematics at the University of Redlands in 2006 and his M.S. in Materials Science and Engineering at UC Irvine in 2007. Weeks’ current research activities include the development of anti-molten-glass infiltration environmental barrier coatings for gas turbine engines and understanding the failure of new fiber-reinforced polymer-matrix composites for radar domes.