Papers by Author: Hong Bo Guo

Abstract: Numerical method was used to simulate the stress state of thermal barrier coatings (TBCs) under thermal-mechanical coupled environment. The finite element (FE) model was built as hollow tube and boundary conditions including heating rate, cooling air convection and mechanical loadings were considered. The maximum stress locates where maximum temperature gradients is formed. This failure mode is consistent with the experimental results.

Abstract: The Hf doped NiAl coatings were co-evaporated and co-deposited onto the superalloy substrate by electron beam physical vapor deposition (EB-PVD). During heat-treatment, HfO2 was formed on the NiAl coatings. And, Hf enriched at the interface between the coating and the interdiffusion zone, which could prevent outward diffusion of elements in the substrate. The NiAl coating doped with 0.5% Hf effectively improved the high temperature oxidation resistance compared to the Hf free NiAl coating and the high Hf content coating. Also, the addition of Hf to the coating contributed to enhancing the adherence of TGO layer to coating.

Abstract: 10mol% Nd2O3 and Yb2O3 co-doped YSZ thermal barrier coatings were produced by electron beam physical vapor deposition (EB-PVD). Compared to the traditional YSZ coating, the deposited coating has shown tree-like microstructure in each column. Due to this, the co-doped coating is more porous than the YSZ coating. The microstructure evolution of the coating during high temperature exposure at 1373 K was studied. The tree-like microstructure disappeared due to joining of sub-grains during sintering. Thermal growth oxide (TGO) grew quickly at the first few hours and then the growth of TGO became slow in the subsequent high temperature exposure. Cracks generated and propagated in the ceramic top coat and along the interface of the top coat and TGO layer. Finally, the coalescence of such cracks resulted in failure of the TBCs.

Abstract: Modified zirconia thermal barrier coatings (TBCs) with segmentation cracks were sprayed onto a TMS 82+ single crystalline substrate. The thermal cycling lifetime of the modified TBC was improved by 10 times compared to that of the traditional non-segmented TBC. Also, the modified coating showed much better resistance to high temperature cyclic hot-corrosion.