Effect of la₂o₃ addition on interface chemistry between 4YSZ top layer and Ni based alloy bond coat in thermal barrier coating by EB PVD

The effect of a 5 mol% La₂0₃ addition on the forming behavior and compositional variation at interface between a 4 mol% Yttria (Y₂0₃) stabilized Zr0₂ (4YSZ) top coat and bond coat (NiCrAlY,) as a thermal barrier coating (TBC) has been investigated. Top coats were deposited by electron beam physical vapor deposition (EB PVD) onto a super alloy (Ni-Cr-Co-Al) substrate without pre-oxidation of the bond coat. Top coats are found to consist of dense columnar grains with a thin interdiffusion layer between metallic bond coats. In the as-received 4YSZ coating, a thin interdiffusion zone at the interface between the top and bond coats was found to consist of a Ni-Zr intermetallic compound with a reduced quantity of Y. Al or O elements. On the other hand, in the case of an interdiffusion area of 5 mol% La₂O₃-added 4YSZ coating, it was found that the complicated composition and structure with La-added YSZ and Ni-Al rich compounds separately. The thermal conductivity of 5 mol% La₂0₃-added 4YSZ coating (∼ 1.6 W/m - k at 1100 °C) was lower than a 4YSZ coating (∼ 3.2 W/m • k at 1100 °C) alone.