Hot corrosion behavior of multi-layer suspension plasma sprayed Gd2Zr2O7/YSZ thermal barrier coatings.

This study investigates the corrosion resistance of double layer Gd₂Zr₂O₇/ /YSZ, triple layer dense Gd₂Zr₂O₇/ / Gd₂Zr₂O₇/YSZ and a reference single layer YSZ coating with a similar overall top coat thickness of 300-320 μm. All the coatings were manufactured by suspension plasma spraying (SPS), resulting in a columnar structure. Corrosion tests were conducted at 900°C for 8 hours using vanadium pentoxide and sodium sulphate as corrosive salts at a concentration of 4 mg/cm₂. SEM investigations after the corrosion tests show that Gd₂Zr₂O₇ coatings exhibited lower corrosion resistance than the reference material, YSZ. Reaction between the corrosive salts and Gd₂Zr₂O₇ results in the formation of gadolinium vanadate (GdVO₄) along the top surface and between the columns. While the stresses due to phase transformation of zirconia can be relieved to some extent by realigning of the columns in the top coat, it is believed that GdVO₄ formation between the columns, along with low fracture toughness of Gd₂Zr₂O₇ had resulted in lower corrosion resistance. Furthermore, the presence of a relatively dense layer of Gd₂Zr₂O₇ on the top, as a preventive layer for salt infiltration, did not improve the corrosion resistance. [ABSTRACT FROM AUTHOR]