Influence of pre-aluminizing on elemental diffusion behavior and fracture mechanism of thermal barrier coatings

Abstract

The development of high-performance aero-engines raises the urgent requirement of coatings deposited on blades, containing both thermal barrier coatings (TBCs) on the external surface and aluminide coatings in the internal winding cooling channels. A TBC system with a low activity aluminizing process before deposition of conventional TBC was developed here to evaluate the feasibility of co-deposition technology. The thermal cyclic oxidation behavior of co-deposited “Al-modified TBC” was examined at 1100 °C and compared to that of conventional TBC. The cross-sectional microstructure evolution and elemental diffusion behavior of the modified TBC were also investigated. Even though the underlying aluminizing layer can serve abundant Al for the upper NiCoCrAlYHf layer to eliminate “Al depletion” in conventional TBC, which is a main reason for spallation, the Al-modified TBC system exhibited shorter thermal cycling life than conventional TBC. The spallation mechanism was discussed. Cracks caused by the fast growth rate of thermally grown oxide (TGO), Cr-rich precipitates resulted from the decreased γ/γ′-phase in the coating, and Re-rich precipitates originated from outward diffusion through the aluminide layer were mainly responsible for the failure.

Keywords

• Aluminizing
• Thermal cycling
• Elemental diffusion
• Fracture mechanism
• Precipitates