Characterization of an Ir-Hf alloy coating as a bond coat material

High temperature oxidation resistance and the topcoat spallation lives of Ir-Hf coated and aluminized Ni-base superalloys are investigated in comparison to Pt coated and aluminized ones. An Ir-Hf binary alloy, proposed as a novel metallic bond coat material, was coated on a Ni-base single crystal superalloy TMS-82 + using electron beam physical vapor deposition followed by a conventional Al pack cementation process. Although cyclic oxidation tests revealed that these Ir-Hf coated and aluminized specimens did not exhibit as good oxidation resistance as the Pt coated and aluminized specimens, formation of TCP phases in the substrate is suppressed by the presence of the Ir-Hf enriched layer. On the other hand, thermal cyclic tests for YSZ coated specimens revealed that Ir-Hf coated and aluminized specimens showed better adhesion to the ceramic top coat layer and demonstrated a longer spallation life than Pt-coated and aluminized specimens, which can be explained by the formation of Al ₂O ₃ and HfO ₂ two-phase structure in the TGO layer. These results indicated that the Ir-Hf alloy system is promising as a new metallic bond coat material for high temperature structural materials.