Influence of Process Parameter on Grit Blasting as a Pretreatment Process for Thermal Spraying

In thermal spraying uncoated substrates usually require roughening. As the most common roughening method, grit blasting increases the surface area and produces undercuts, which facilitate mechanical interlocking and thus promote the bonding between the substrate and coating. The effects of grit blasting parameters, i.e. the particle size, the blasting angle, the stand-off distance and the pressure, on the resulting surface topography are investigated. Furthermore the efficiency and wear behavior of the blasting media are analyzed. Influences of three different blasting media, corundum, alumina zirconia and steel shot, on the surface roughening are compared. In order to study the correlation between surface roughness and the bond strength, the surface topography of grit blasted samples are examined using confocal laser scanning microscopy. These samples are then coated and tested by means of adhesion tests (PAThandyTM) to identify the topography characteristics as well as pretreatment parameters which promote a good bond strength.