Improving the thermal shock resistance of plasma sprayed CYSZ thermal barrier coatings by laser surface modification

In this study, substrates of Inconel 738 LC superalloy coupons were first sprayed with a NiCoCrAlY bondcoat and then with a ceria and yttria stabilized zirconia (CYSZ) topcoat by air plasma spraying (APS). After that, the plasma sprayed CYSZ thermal barrier coatings (TBCs) were treated using a pulsed Nd:YAG laser. The effects of laser glazing on the microstructure and thermal shock resistance of the coatings were evaluated. Thermal shock test was administered by holding specimens at 950 °C for 5 min and then water quenching. More than 20% of the spalled region of the surface of the topcoat was adopted as the criterion for the failure of samples. The microstructures of both the as processed and the tested TBCs were investigated using scanning electron microscope (SEM). The phases of the coatings were analyzed with X-ray diffractometry (XRD). XRD analysis revealed that both as sprayed and laser glazed topcoats consisted of nonequilibrium tetragonal (T′) phase. The results showed that the life times of the as sprayed TBCs were enhanced around fourfold by the formation of a continuous network of segmented cracks perpendicular to the surface and the increase in strain accommodation.