Laser Surface Texturing of Nickel Superalloy to Improve Adhesion Bond Strength of Thermal Barrier Coating

Abstract

Laser surface texturing was adopted as a strategy to improve the adhesion bond strength of thermal barrier coating generally used in aero turbine components. A picosecond Q-switched Nd: YAG laser operated at 532 nm wavelength was used to perform laser surface texturing. Two different types of texture namely, oriented square pattern having 250 µm width and 250 µm pitch and trapezoidal pattern having 150 µm width and 250 µm pitch were textured on nickel superalloy C-263 surface prior to air plasma spraying of NiCrAlY bond coat. The microstructure and surface morphology of these patterns were characterized by Optical Microscope (OM) and White Light Interferometer (WLI). The presence of pre-defined texture in the laser ablated region and greater surface contact enhanced the mechanical interlocking with the bond coat. The generation of grooves increased the surface roughness of textured substrate 6 times greater than grit blasting. Further, the trapezoidal pattern exhibited higher surface roughness due to greater laser ablated area. The adherence was tested by adhesion bond strength test which showed 35 MPa and 37 MPa adhesive strength for oriented square and trapezoidal pattern, respectively. The fractal analysis showed that the textured substrate failed predominantly by cohesion.