Role of Powder Granulometry and Substrate Topography in Adhesion Strength of Thermal Spray Coatings

APS coating is deposited with different treated surfaces to understand the effects of surface topography and particle sizes on adhesion bond strength. Grit blasting and laser surface texturing have been used to create a controlled roughness and controlled surface topography, respectively. Coating adhesion is mainly controlled by a mechanical interlocking mechanism. Fully melted Ni-Al powder fills the respected target surface with high-speed radial flow. Pores around central flattening splat are usually seen due to splash effects. Laser surface texturing has been used to study near interface coating depending on the target shape and in-contact area. Pull-off test results have revealed predominant correlation with powder, surface topography, and adhesion bond strength. Adhesion bond strength is linked to the in-contact area. So, coating adhesion might be optimized with powder granulometry. Pores near the interface would be localized zones for crack initiations and propagations. A mixed-mode failure has been reported for sharp interface (interface and inter-splats cracks) due to crack kicking out phenomena. Coating toughness near the interface is a key issue to maximize adhesion bond strength. Volume particles and topography parameters have been proposed to enhance adhesion bond strength for thermal spray process for small and large in-contact area.