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 bond coat and top coat and (ii) bond coat oxidation. Both of these can cause 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-layer TBC consisting of an MCrAlY bond coat, an Al2O3, diffusion barrier (2-5 mu m) and a ZrO2-Y2O3 top coat are presented. The diffusion barrier is applied by the r.f. physical Vapour deposition process; the bond coat and top coat by plasma spraying. By the use of a diffusion barrier the bond coat oxidation can be strongly reduced in the tested temperature range from 1173 to 1373 K. The oxidation kinetics are influenced by the thickness of the diffusion barrier, the temperature of oxidation and the bond coat composition. TBC systems with high oxidation resistance show the best ceramic-bond coat interface strength.