Abstract No.:
4606

 Scheduled at:
Wednesday, May 11, 2016, Room 3H + 3I + 3J 9:20 AM
Power Generation I


 Title:
Hot corrosion behavior of suspension plasma sprayed multilayer Gd2Zr2O7/YSZ thermal barrier coatings

 Authors:
Krishna Praveen Jonnalagadda* / Linköping University, sweden
Satyapal Mahade/ University West, Sweden
Xin-Hai Li/ Siemens Industrial Turbomachinery AB, Sweden
Nicolaie Markocsan/ University West, Sweden
Stefan Björklund/ University West, Sweden
Nicholas Curry / Treibacher Industrie AG, Austria
Per Nylén/ University West, Sweden
Ru Lin Peng/ Linköping University, Sweden

 Abstract:
The corrosion resistance of multi-layer thermal barrier coatings (TBC) with gadolinium zirconate (Gd2Zr2O7) is investigated in the current work. TBC samples of double layer Gd2Zr2O7/YSZ (yttria stabilized zirconia), triple layer dense Gd2Zr2O7/Gd2Zr2O7/YSZ and a reference single layer YSZ coating with a similar overall thickness of 300µm were manufactured by suspension plasma spraying (SPS), resulting in a columnar structure. Corrosion tests were conducted at 900oC for 8 hours using vanadium pentoxide and sodium sulphate as the corrosive salts at a concentration of 4mg/cm2. XRD examinations of the top surfaces and SEM analysis of the cross-sections were performed on the as corroded samples. It was found that the Gd2Zr2O7 coatings have significantly lower corrosion resistance than the reference material, YSZ. Reaction between the corrosive salts and Gd2Zr2O7 resulted in the formation of gadolinium vanadate (GdVO4) along the top surface and between the columns, accompanied by phase transformation of zirconia from cubic to monoclinic. While the stresses due to phase transformation of zirconia can be relieved to some extent by realigning of columns in the top coat, it is believed that GdVO4 formation along with the low fracture toughness of Gd2Zr2O7 had caused damage to the coating. Furthermore, the presence of a thin dense layer of Gd2Zr2O7 on the top, as a preventive layer for salt infiltration, did not seem to reduce the corrosion induced damage.

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