Improvement of thermal plasma sprayed coating adhesion strength by laser microtexturing of aluminum

Abstract

Abstract Surface microtexturing improves coating adhesion strength due to increased surface area and mechanical interlocking. Grit blasting and laser processing are two common methods used for surface microtexturing. Laser microtexturing offers distinct advantages over grit-blasting as it improves interface quality, provides a grit-particle-free surface, optimized processing time, and greater control over the surface roughness. This paper reports a full area method of laser microtexturing of Al 7075 alloy using a nanosecond pulsed laser to generate a large increase in surface area. This method involves a laser-induced thermo-mechanical process where tightly packed pillar-like surface features were formed due to the surface melting and re-solidification of materials combined with some ablation. The morphology of the microtexture was controlled by varying the laser processing parameters. Thereafter, the laser microtextured surface was coated with metallic coatings using thermal spray. Our method is superior to the currently used laser ablation-based microtexturing method. The surface morphology, composition, and adhesion strength results are presented. The tensile adhesive strength of the thermally sprayed metallic CoNiCrAlY coating was measured, and an improvement of over 17% in the coating adhesion strength was observed for a 5 µm deep microtexture compared to that of grit-blasted samples. This is the highest reported adhesion strength for thermally sprayed bond coating.