Knowledge Oriented Materials Engineering of Layered Thermal Barrier System (Nomelt)

: A team from academia, Air Force laboratories and industry has been assembled to develop a design code for one of the prevailing failure modes in thermal barrier systems used for aero-turbines. The failure mechanism to be addressed occurs in systems with two-phase bond coats and is manifest as abrupt delamination along the interface between the thermally grown oxide (TGO) and the intermetallic bond coat. The code will integrate several important time/cycle dependent phenomena, each with associated constituent models for: interface adhesion, bond coat deformation, sintering in the thermal barrier layer, etc. In this the second year of the project, efforts have focused on experimental characterization of the various layers and the development of hierarchical models, both of which are needed to characterize and define the salient governing phenomena. A previously developed interfacial delamination model is being adapted for this problem, and integration of these efforts will provide the pathway to the TBC design code. The focus of the University of Michigan effort was on (1) the evolution of the bond coat structure and properties during elevated temperature exposure under oxidizing conditions and (2) the development of a new apparatus for studying the failure process during cyclic oxidation of the MCrAlY class of coatings. Background and motivation for this research are first reviewed and a summary of results in the above two areas is given.