Fracture and Fatigue Crack-Growth Behavior of Interfaces in Thermal Barrier and Wear Resistant Coating Systems

摘要

The research on the fracture and fatigue crack-growth behavior of single crystal intermetallics was motivated by the need for improved high temperature engineering materials. The approach using a first principles total energy calculation of the energies of .001. and .110. surfaces in NiAl, by Yoo and Fu predicts very low fracture toughness vs. experimental findings. As the program has developed, the focus has shifted to the use of thermal barrier and wears resistant coatings to improve material behavior at high temperature and other extreme service conditions. The present emphasis therefore to develop thermal barrier and wear resistant coating systems with improved integrity and long term reliability. The major accomplishment of this work has been the development of fracture-mechanics based techniques to accurately and reproducibly measure the fracture resistance (or adhesion) of coating systems. We believe the data presented to be unique for the two coating systems characterized. Interface toughness, K, data was obtained for several specimens containing multi-layer systems of PSZ-NiAl-Pt- Superalloy and TiAlN-Cermet. The interfaces prone to fracture were identified. Experiments were also completed to analyze crack-growth under cyclic fatigue loading of these interfaces.