Evaluation of microstructure and coating integrity of EB-PVD deposited bi-layers of 7YSZ/Gd2Zr2O7 and 7YSZ/Y2O3-Gd3Zr3O7 top coats on bond coated superalloys

In the present study, 7YSZ/gadolinium zirconate (GZ) and 7YSZ/2.3 wt.% yttria doped gadolinium zirconate (YGZ) bi-layers were deposited onto the plasma sprayed bond coated Inconel-718 substrates by EB-PVD technique. Structural analysis revealed that GZ and yttria doped GZ has thermally stable pyrochlore structure and no phase transformation was observed even after thermal cycling test at 1523 K up to 75 cycles. Vicker's microhardness measurements of the coatings indicated that yttria doped GZ had improved mechanical properties than that of GZ. Hot corrosion behaviour of 7YSZ/GZ and 7YSZ/Y-GZ were evaluated with the mixture content of 45 wt.% of Na2SO4 and 55 wt.% V2O5 at 1273 K. Failure analysis of these TBCs was investigated by isothermal oxidation test (1273 K) and thermal cyclic test (1523 K). The results revealed that bi-layered 7YSZ/yttria doped GZ showed improved performance than that of the bi-layered 7YSZ/GZ TBC.

Automated summary

A study was conducted to deposit 7YSZ/gadolinium zirconate (GZ) and 7YSZ/2.3 wt.% yttria doped gadolinium zirconate (YGZ) bi-layers onto Inconel-718 substrates using the EB-PVD technique. The structures of GZ and yttria doped GZ coatings were found to be thermally stable, with no phase transformation observed after thermal cycling. Vicker's microhardness measurements showed that yttria doped GZ had better mechanical properties than GZ. The hot corrosion behavior of the bi-layered coatings was evaluated and it was found that the 7YSZ/Y-GZ showed improved performance compared to the 7YSZ/GZ TBC.