Assessment of Adhesion Characteristics of Thermal Barrier Coatings Using Scratch Test

Abstract

Thermal barrier coatings (TBCs) are advanced materials usually applied to a variety of applications involving high temperature and oxidation such as gas turbines. It is commonly used as protective coatings to improve performance, protect metallic components at elevated temperature and allow higher operating temperatures beyond the limiting temperature of structural components. TBCs structure consists of four layers such as ceramic topcoat, usually 8wt% of YSZ; thin layer of thermally grown oxide (TGO) formed during the service; the metallic bond coat, usually MCrAlY and the metal substrate, usually Ni-based superalloy. The adhesion between the top coat/bond coat interface is an important property in TBCs system. The TGO formed during the service between the top coat/bond coat interface is a necessary layer of a TBC system, providing an oxidation barrier for the underlying component. Unfortunately, TGO is also the main driver of failure in TBC systems, which affects the adhesion of top coat/bond coat. However, the adhesion characteristic of TBCs are not well understood. In this work, new approaches to better understand the adhesion of TBCs by using the scratch test based on the Burnett and Rickerby model was used. The relationship between the adhesion of the top coat/bond coat and TGO formed during service was investigated. The cycle thermal fatigue test was used to reproduce the working condition of the TBCs system in the hot section. TBCs were also investigated the lifetime and failure characteristics after the thermal cycle fatigue test. The outcomes of this work may provide a useful guideline for work of adhesion characteristic of TBCs using the scratch test. In addition, the results of this work were expected to be useful to gain an in-depth understanding of the most probable combination and identifying a relationship of the work of adhesion with the thermal cycle fatigue test to use in a life prediction model.