Pull-off adhesion testing is a commonly used method to determine the coating adhesion strength. Relying on the pull-off adhesion testing technique to determine the coating adhesion strength is increasingly common due to its quantitative result. This study focuses on how the pull-off adhesion strength value of the coating is affected by the change in critical factors i.e. surface profile morphology (spherical, sharp & angular) and a range of surface roughness profile height (μm). Test sample surface was prepared to visually clean steel with diverse sizes and shapes of abrasives, coated with a 3 coat system. Pull-off adhesion testing was performed on the fresh coating and after exposing the coating to cyclic ageing test conditions adopted from ISO12944-9, Annex B. Additionally, electrochemical impedance spectroscopy (EIS) and surface characterization of abrasives using scanning electron microscopy (SEM) and cross sectional analysis of coating sample after ageing with SEM-EDS (Scanning electron microscopy-Energy dispersive spectroscopy) were also performed.
Coatings have been used as a primary method to protect the substrate underneath from corrosion in various geographical environments. A diverse range of generic coating types are available to protect the metals in different corrosive environments. Selection of the right coating for a specific metallic substrate at given operating conditions and environment is key to avoiding any premature failures of coating. Incorrect coating application can lead to costly rework, schedule delays and substandard performance than intended for1. Good adhesion of coating with its substrate is one of the key characteristics for a coating system to achieve its design lifetime2, 3. In other words, the coating performance is dependent on its ability to remain well adhered to the substrate4. If the primer coat did not achieve good adhesion with the substrate, it would peel or delaminate and take with it all the layers above it5. Adhesion of coating is defined as the resistance of coating against mechanical separation from the substrate6. Generally, coatings applied as per manufacturer recommendations offer good adhesion to the substrate and can resist the permeation of corrosive species. On the contrary, when coatings were exposed to corrosive elements (UV, chloride ions, temperature etc.) coating adhesion was reported to decrease due to the coating degradation caused by UV exposure and permeation of chloride ions through the coating to the substrate4, 7, 8. Corrosion has less impact on the overall integrity of coated structure if superior adhesion is achieved9.
