On the role of imperfections in the failure of a thermal barrier coating made by electron beam deposition

An impression test has been used to explore the remnant toughness and the d elamination characteristics of thermal barrier coatings (TBCs) after extend ed thermal exposure. The delamination trajectory is found to change as the thermally grown oxide (TGO) thickens. At small thicknesses, delamination oc curs predominantly within the TGO and TBC. With a thicker TGO, developed af ter 100 h exposure at 1100 degrees C, the delamination extends predominantl y along the TGO/bond coat interface, but with small oxide domains remaining embedded in the bond coat. The changes in the interface adhesion and the m echanics responsible for this transition are addressed, along with a discus sion of the role of morphological imperfections in the TGO in failure nucle ation. A method for determining the effective in-plane modulus of the TBC f rom the curvature of decohered TGO/TBC bilayers is also presented. (C) 2000 Acta Metallurgica Inc. Published by Elsevier Science Ltd All rights reserv ed.