Hot corrosion behavior of multi-layer suspension plasma sprayed Gd_2Zr_2O_7/YSZ thermal barrier coatings

摘要

This study investigates the corrosion resistance of double layer Gd_2Zr_2O_7/YSZ, triple layer dense Gd_2Zr_2O_7 / Gd_2Zr_2O_7/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 Gd_2Zr_2O_7 coatings exhibited lower corrosion resistance than the reference material, YSZ. Reaction between the corrosive salts and Gd_2Zr_2O_7 results in the formation of gadolinium vanadate (GdVO_4) 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 GdVO_4 formation between the columns, along with low fracture toughness of Gd_2Zr_2O_7 had resulted in lower corrosion resistance. Furthermore, the presence of a relatively dense layer of Gd_2Zr_2O_7 on the top, as a preventive layer for salt infiltration, did not improve the corrosion resistance.