Abstract
Rare earth oxide doping zirconate ceramics are a new kind of thermal barrier coatings (TBCs) materials that can be suitable for higher service temperature. Single layer (Yb0.1Gd0.9)2Zr2O7 ceramic coatings were fabricated onto both of (Ni, Pt)Al and Cr-modified (Ni, Pt)Al bond coat surfaces. The microstructure, interface elemental diffusion, residual stress as well as isothermal oxidation behavior of two TBCs specimens were evaluated. The compact and uniform Cr-modified layer can act as a diffusion barrier, effectively preventing Al element from diffusing to the bond coat surface. The thickness of pre-oxidation layer grown at the interface between Cr-modified (Ni, Pt)Al and (Yb0.1Gd0.9)2Zr2O7 is relatively thin, which is measured to be only ∼140 nm. With the prolonging of oxidation durations, the surface microcracks' width and sintering morphology of Cr-modified (Ni, Pt)Al TBCs are obviously less severe than that of (Ni, Pt)Al TBCs. The modification effect of Cr onto (Ni, Pt)Al surface is also reflected in the decrease of the thickening rate of thermally grown oxide (TGO) and the improvement durability of β phase within bond coat. Although the residual stress in TGO layer of Cr-modified (Ni, Pt)Al TBCs increases continuously during thermal exposure from 200 h to 700 h, no serious microcracks' propagation occurs on the surface of (Yb0.1Gd0.9)2Zr2O7 coating. The ceramic coat of (Ni, Pt)Al TBCs spalls extensively and further the TGO exhibits a double-layer structure when the isothermal oxidation is carried out up to 700 h. In that TGO morphology, the columnar crystals are observed near the bond coat, while the fine equiaxed grains are detected approach to the ceramic coat. In comparison, the bond coat of Cr-modified (Ni, Pt)Al with (Yb0.1Gd0.9)2Zr2O7 ceramic topcoat has better interlayer matching, and such TBCs shall have the potential to provide thermal protection for the superalloy substrate even after 700 h of isothermal oxidation.
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