Oxidation and hot corrosion resistance of HVOF/EB-PVD thermal barrier coating system

Hot corrosion and oxidation cause very destructive damage in thermal barrier coatings (TBCs) during service conditions. In hot corrosion, TBCs exposed to molten salts lose their integrity easily due to the phase transformations while oxygen easily penetrates from the TBCs to bond coats and forms thermally grown oxide (TGO) layer which causes higher stresses at the interface of bond and top coating. In the current study, CoNiCrAlY powders were sprayed by high-velocity oxygen fuel (HVOF) technique on Inconel 718, and then yttria-stabilized zirconia (YSZ) and YSZ/Gd2Zr2O7 ingots were deposited by electron beam physical vapor deposition (EB-PVD) technique on the bond coated substrates. Isothermal oxidation tests were carried out at 1000 °C for 8, 24, 50, and 100 h, while hot corrosion tests were carried out at 1000 °C in the presence of NaCl, Na2SO4, and V2O5 molten salts with 5, 10, 15, and 20 h cycles. The produced coatings, as well as the oxidation and hot corrosion test results, were examined using SEM, EDS, XRD, and image analysis techniques. After the tests, the Gd2Zr2O7 layer was found to exhibit superior oxidation and hot corrosion performance as compared to the conventional YSZ TBC system. •β-NiAl phases slightly depleted after oxidation tests and, the TGO layer dominantly composed of alumina.•The phase transformation or spallation were not observed after the oxidation test.•YVO4 and GdVO4 phases led to the phase transformation in the top coatings after the hot corrosion tests.•Gd2Zr2O7 layer completely spalled from YSZ layer while YSZ TBC was still compact at the end of the hot corrosion tests.