Hot corrosion behavior of laser-glazed plasma-sprayed yttria-stabilized zirconia thermal barrier coatings in the presence of V 2O 5

Abstract

Thermal barrier coatings (TBCs) are now currently used in gas turbine engines' blades and vanes. A typical duplex TBCs system comprises of a plasma-sprayed thermally insulating ZrO 2 alloy top coat applied over an oxidation-resistant MCrAlY (M = Ni and/or Co) bond coat. In this investigation, the substrates of Hastelloy-X superalloy coupons were first sprayed with a Ni–22Cr–10Al–1Y bond coat and then with an yttria-stabilized zirconia (YSZ) top coat in which the yttria contents were varied from 6.1 wt.% to 19.5 wt.%. After that, the plasma-sprayed yttria-stabilized zirconia/MCrAlY TBCs were glazed using a pulsed CO 2 laser. The hot corrosion resistance of plasma-sprayed and laser-glazed zirconia thermal barrier coatings at 910 °C was investigated using coupons on which were deposited Na 2SO 4 and/or V 2O 5. The results of the high temperature corrosion tests showed that the lifetimes of the plasma-sprayed TBCs with different yttria content were all increased about fourfold by laser-glazing in the V 2O 5 salt contained test. The lifetime decreased with increasing the amount of deposited V 2O 5 salt. The X-ray diffraction showed that the reaction between yttria (Y 2O 3) and V 2O 5 produced YVO 4, leaching Y 2O 3 from the YSZ and causing progressive cubic, tetragonal to monoclinic phase destabilization transformation. The failure of the TBCs was initiated and propagated mainly within the top coat, near the top coat–bond coat interface. Both adding Na 2SO 4 and a reaction between Na 2SO 4 and the bond coat can probably reduce the strain accommodation of the top coat. There are no significant corrosion cyclic life differences for TBC with various YSZ top coats for both plasma-sprayed and laser-glazed TBC.