THERMAL BARRIER COATINGS WITH IMPROVED OXIDATION RESISTANCE

The lifetime of thermal barrier coatings (TBCs) is limited by two main failure mechanisms, namely (i) thermal expansion mismatch between bon d coat and top coat and (ii) bond coat oxidation. Both of these can ca use failure of the ceramic top coat. Developments of recent years show that bond coats with higher oxidation resistance lend to have better coating system cyclic lives. In this paper the properties of a three-l ayer TBC consisting of an MCrAlY bond coat, an Al2O3, diffusion barrie r (2-5 mu m) and a ZrO2-Y2O3 top coat are presented. The diffusion bar rier is applied by the r.f. physical Vapour deposition process; the bo nd coat and top coat by plasma spraying. By the use of a diffusion bar rier the bond coat oxidation can be strongly reduced in the tested tem perature range from 1173 to 1373 K. The oxidation kinetics are influen ced by the thickness of the diffusion barrier, the temperature of oxid ation and the bond coat composition. TBC systems with high oxidation r esistance show the best ceramic-bond coat interface strength.