Effect of the width and depth of laser-textured grooves on the bonding strength of plasma-sprayed coatings in the scratch direction

In this study, atmospheric plasma spraying was used to deposit molybdenum coatings on stainless steel substrates with laser-textured groove patterns and grit blasting substrate pretreatment. The groove depth and width were controlled by selecting the number of scans with a nanosecond pulse laser (1, 3, 5, and 7), while the groove spacing was 100 μm, 150 μm, and 200 μm. The pull-off bonding strength and shear bonding strength parallel and perpendicular to the grooves of the coatings were analyzed using a pull-off and scratch instrument. Furthermore, optimal laser scan times of the groove opening angle were obtained. The results showed that the coating adhesion strength on the grooved substrate with a 100 μm spacing and 5 scans was greater than the cohesive strength. On the other hand, the pull-off bonding strength of coatings on the substrates made with 5 and 3 scans was superior to that on the grit-blasted stainless steel substrate; furthermore, the shear bonding strength in parallel and perpendicular scratch directions of the coating made on the grooved substrate with 5 scans was greater than that on the grit-blasted substrate; for all textured substrate coatings, the shear bonding strength in the parallel direction higher than that in the perpendicular direction. Finally, the equations that correlate the groove width, opening angle, pull-off bonding strength, shear bonding strength, and scanning times were predicted. The study provides significant experimental findings and a theoretical basis about the bonding strength of the laser-textured substrate plasma spraying coatings.