Influence of the Abrasive Reuse on Surface Preparation by Grit Blasting for Thermal Spray 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, alumina was used to blast surfaces in order to show the influence of the abrasive reuse on the decrease in granulometry, surface roughness 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. Sa, Sz, SSk and SKu were the parameters chosen for the roughness characterization and were compared to the grain size loss, 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 after the third cycle there was a decrease in roughness, affecting the adhesion strength. In conclusion, the small fraction of grit with decreased granulometry present reduces the effectiveness of the process.