Thermal barrier coatings for the 21st century

Yttria stabilized zirconia (YSZ) thermal barrier coatings (TBCs) fabricated via electron beam physical vapor deposition (EBPVD) provide some unique pr operties for aerofoil applications. Such coatings are usually deposited on diffusion aluminide or MCrA1Y bond coats on superalloy substrates. During d eposition of the YSZ-TBC on the bond coat, a thermally grown oxide (TGO) co nsisting primarily of alpha-Al2O3 is formed between the TBC and bond coat. The lives of these TBCs in oxidizing environments is deter mined by the int erplay of the stored elastic energy driving spallation versus the interfaci al toughness of the TGO/bond coat interface since failure of the TBC system often occurs at this interface. The microstructures of EBPVD-TBCs in the a s-processed and exposed conditions have been documented using a variety of techniques to determine and describe the failure mechanisms. It is shown th at the failure mechanisms for TBC's are dependent on the bond coat fabricat ion procedure and the exposure environment. Finally, possible schemes for i mproving TBC systems are outlined.