Multi-layered thermal barrier coatings fabricated by plasma-spraying and dry-ice blasting: Microstructure characterization and prolonged lifetime

The quality of bond coat and top coat of thermal barrier coatings (TBCs) has strong influences on their lifetime at high temperature. Especially, the oxygen content level and the surface roughness of bond coat as well as the porosity of top coat have been demonstrated to play an important role in the thermomechanical behavior of TBCs. In this study, dry-ice blasting was used during the preparation of TBCs which were composed of atmospheric plasma sprayed CoNiCrAlY bond coat and YSZ top coat. Three sets of TBCs deposited with different dry-ice (CO2) blasting treatments were compared with respect to the coating microstructure evolution, the growth behavior of thermally grown oxide (TGO), crack propagation and thermal shock resistance during thermal cycling exposure. It was interesting to find that different microstructures of bond coat and top coat were obtained under different spraying conditions. Moreover, the results showed that CoNiCrAlY bond coats continue to be oxidized during the deposition process of YSZ top coats when they are plasma-sprayed without dry-ice blasting. The three sets of prepared TBCs have different thermal shock lifetime. TBC with APS dry-ice blasted bond coat and APS dry-ice blasted top coat was the most durable and exhibited significant improvement in lifetime. The remarkable decrease in the oxide content and the porosity of bond coat, the increase in the “vertical” porosity of top coat and the improvement in the bonding strength at the bond coat/top coat interface appeared to contribute to the prolonged lifetime.