Microstructure design and mechanical properties of thermal barrier coatings with layered top and bond coats

The microstructure of layered thermal barrier coatings (TBCs) with three coating layers in the bond and top coats, respectively, prepared using a specialized coating system (TriplexPro™-200), was controlled and its mechanical properties were investigated, which were then compared with the common TBCs with a single layer in each coat. The bond and top coats were coated with 100 and 200 μm for each feedstock, resulting in 300 and 600 μm thicknesses in the bond and top coats, respectively. The microstructure of the top coat could be controlled by changing the feedstock and using a multiple hopper system—dense/intermediate/porous layers from surface to interface or reverse microstructure. In the case of the bond coat, a compositional gradient was achieved. The adhesive strength values of the top coats were strongly dependent on the microstructure, whereas the values for the bond coat were similar. The hardness and toughness values gradually changed from surface to interface, indicating that the mechanical properties corresponded well with the microstructure of the TBCs. The indentation stress–strain curves of both TBCs with the layered structure were located between the curves for TBCs with the single structure of relatively dense and porous microstructures. Damage on the surface and subsurface was strongly affected by the microstructure of the top coat, showing a similar trend with the stress–strain behavior. This evidence allowed us to propose an efficient coating in protecting the substrate from mechanical environments.