Microstructure and Properties of Peg-nail Structured YSZ TBCs by Selective Laser Modification after Plasma Spraying

Abstract

Yttria partially stabilized zirconia (YSZ) thermal barrier coatings (TBCs) were deposited by an air plasma spraying (APS) method on nickel-based superalloy with initially sprayed NiCoCrAlYTa bond coat. After that, the surface of the plasma sprayed TBCs was subjected to selective laser modification using a Nd:YAG pulsed laser. The microstructure and performance of the plasma sprayed and peg-nail structured YSZ coatings by selective laser modification were investigated. The results reveal that selective laser modification helps to reduce the surface roughness considerably, eliminate surface porosities and produce a network of continuous cracks perpendicular to the surface. The microstructure of peg-nail structured units consists of columnar grains in the cross-section and equiaxed grains on the surface. XRD patterns show that both as-sprayed and the peg-nail structured coatings by selective laser modification consist of nonequilibrium tetragonal (T') phase; however, monoclinic (M) phase disappeared and intensity of T' phase slightly increases in the range of 72°∼76°(2 θ ) after selective laser modification. It has been found that the average bonding strength YSZ coatings is enhanced from 7.3 MPa to 13.3 MPa after selective laser modification. Thermal insulation capability of the peg-nail structured YSZ coating by selective laser modification, as compared to the as-sprayed YSZ coating, is decreased due to microstructure change in the ceramic top coat.