High temperature corrosion resistance and microstructural evaluation of laser-glazed plasma-sprayed zirconia/MCrAlY thermal barrier coatings

Plasma-sprayed yttria-stabilized zirconia/MCrAlY thermal barrier coatings (TBCs) were laser-glazed using a pulsed CO2 laser. The high temperature corrosion resistance of plasma-sprayed and laser-glazed zirconia thermal barrier coatings at 910 °C was investigated using coupons on which Na2SO4 and/or V2O5 were deposited. The microstructures of both the as-deposited and the tested TBCs were examined with scanning electron microscopy (SEM). The phase transformation and microstructure of the coatings were studied using X-ray diffractometry (XRD) and an electron probe microanalyzer (EPMA). Experimental results indicated that neither spallation nor buckling occurred in the Na2SO4-deposited samples after 62 h of cycling. The lifetimes of the plasma-sprayed TBCs were enhanced approximately fourfold by laser glazing in tests that involved V2O5 salts. The lifetime declined with an increasing amount of deposited V2O5 salt. The failure of the TBCs was initiated and propagated mainly within the top coat near the alumina–zirconia interface. X-Ray diffraction showed that the reaction between yttria (Y2O3) and V2O5 produced YVO4, leaching Y2O3 from the yttria-stabilized zirconia (YSZ) and causing progressive cubic 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. Improving the strain accommodation through segmented cracks produced by laser-glazing and reducing the penetration of the molten V2O5 by laser-glazed layer are the major mechanisms for extending the lifetime of the TBC.