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

Abstract

Plasma-sprayed yttria-stabilized zirconia/MCrAlY thermal barrier coatings (TBCs) were laser-glazed using a pulsed CO 2 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 Na 2SO 4 and/or V 2O 5 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 Na 2SO 4-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 V 2O 5 salts. The lifetime declined with an increasing amount of deposited V 2O 5 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 (Y 2O 3) and V 2O 5 produced YVO 4, leaching Y 2O 3 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 V 2O 5 by laser-glazed layer are the major mechanisms for extending the lifetime of the TBC.