Influence of aluminium on the valence electron density of the interface between the bond-coat and the thermally grown oxide of thermal barrier coatings

The interface cohesion greatly affects the longevity of thermal barrier coatings (TBCs). The adherence and stress of the interface between the bond-coat and the thermally grown oxide (TGO) are considered as crucial properties governing the life times of TBCs. In this paper, the electron density of the bond-coat/TGO interface of TBCs was calculated with the empirical electron theory in solid and molecules. The calculation results of the electron density of the bond-coat/TGO interface with various bond-coat aluminium contents were analyzed in the views of interface bonding force, interface stress and interface stability. It is shown that the suitable aluminium content of the bond-coat should be in the ranges of 8–10wt% and about 2wt% considering the bond-coat/TGO interface only. Taking the bond-coat/top-coat interface of TBCs into account, combining the consideration of the TGO forming ability, the suitable aluminium content becomes about 8wt% and a little less than 8wt%, which accords better with actual TBC applications. The deduction not only can be a useful reference to the composition design of the bond-coat of TBCs, but also shows the necessity of considering the electron density parameters of the interfaces of bond-coat/top-coat and bond-coat/TGO simultaneously in the composition design of the bond-coat of TBCs.