Influence of Aluminum Oxide Grit Reuse on Surface Preparation and Bond Strength of Thermally Sprayed Coatings

Thermally sprayed coatings rely on mechanical anchoring as the main bond mechanism, which depends on previous surface preparation, i.e. cleaning, roughening and preheating. In this work, aluminum oxide (Al2O3) grit was used to blast surfaces in order to show the influence of the abrasive reuse on the decrease in granulometry, surface roughness, cleanliness and consequently on the coating adhesion strength. SEM images illustrate the difference in grain sizes and EDS was used to study the contamination of the abrasive with the substrate elements. To understand the granulometry reduction, the samples were blasted and after each cycle the abrasive was classified with different sieves, and then the mass was measured. The abrasive was mixed and the process was repeated for five cycles. S-a, S-z, S-sk and S-ku were the parameters chosen for the roughness characterization and were compared to the grain size decrease, showing a significant correlation between them. Lastly, the adhesion strength of the coatings was measured according to ASTM-C633 and compared to both the roughness and blast cycle. The results show that a small fraction of abrasive with finer grit reduces the roughness significantly. However, the adhesion strength was not affected.