Influences of Microstructure Defect Size and Distribution for Performance Optimization of Thermal Barrier Coatings

Abstract

Thermal barrier coatings are often used to protect a component by reducing temperature excursions. Such coatings are in use on engineered products such as turbine blades. The work presented is part of a broader effort that is focusing on new and novel processing techniques for thermal barrier coatings. Manufacturing methods are being developed to create microstructures that optimize thermal protection while not degrading the mechanical properties of the coating. Sufficient mechanical properties are necessary so the coatings do not fail as a result of loadings associated with the operation of the component. One fabrication method investigated is the inclusion of spherical micron-sized pores to reflect heat radiation at high temperatures along with nano-sized grains to reflect phonons thus providing thermal protection. Pores are sized and distributed so that sufficient mechanical strength is maintained. In the current work the model material used is a yttria-stabilized zirconia (YSZ). Two-dimensional microstructures representing YSZ are computationally generated. The size and distribution of defects that have been experimentally observed to develop during bulk processing are incorporated into the computationally generated microstructural models. Heat transfer and stress-displacement analyses are performed to determine effective bulk material properties. Comparisons are made to experimental measurements available in the literature as appropriate. The influence that defect dimensions and distributions have on the effective bulk material properties are quantified as a first step understanding the impacts that micron sized pores, voids and cracks have on thermal and mechanical characteristics which will facilitate optimizing the microstructure for thermal protection and strength retention.