Comparison of microstructural characteristics and hot corrosion behavior of APS- and SPS-deposited YSZ and Gd2Zr2O7/YSZ thermal barrier coatings

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This work compares the microstructural characteristics and hot corrosion behavior of single-layer yttria-stabilized zirconia (YSZ) and double-layer Gd 2 Zr 2 O 7 (GZ)/YSZ thermal barrier coatings (TBCs). Two deposition techniques were employed, specifically conventional atmospheric plasma spraying (APS) and a suspension plasma spraying (SPS) process. Microstructural analysis performed via scanning electron microscopy (SEM) showed two distinct as-sprayed TBC architectures: SPS produced coarse columnar structures, whereas APS provided porous lamellar microstructures comprising splats solidified parallel to the base. Hot corrosion tests were conducted under cyclic conditions at 950 °C for 4 h in Na 2 SO 4 +V 2 O 5 corrosive salt mixture, which typically occur under TBC operating conditions. The related hot corrosion mechanisms of the TBC systems were investigated using X-ray diffraction (XRD) and SEM equipped with energy dispersive X-Ray spectroscopy (EDXS). The reference single-layer YSZ coating experienced more extensive damage due to the leaching of Y 2 O 3 from the YSZ structure, accompanied by the formation of YVO 4 corrosive products and the phase transformation of tetragonal to monoclinic ZrO 2 . In the double-layer GZ/YSZ coatings, the molten salt reacted first with the topcoat material (Gd 2 Zr 2 O 7 ) to form GdVO 4 crystal structures. As a result, the molten salt infiltration into the YSZ structure was delayed, thereby enhancing the hot-corrosion protection and structural integrity of the studied TBC systems. The work also provides a detailed comparative analysis of the corrosion mechanisms observed in the APS- and SPS-deposited coatings.