Effect of grit-blasting parameters on the surface roughness and adhesion strength of sprayed coating

Surface preparation is very important in adhesive bonding of spray coatings to the surface of a work piece. The common practice is grit blasting of the surface before subjecting it to the spray coating process. In this study, grit blasting of an AISI 4130 steel (of different heat treatments) with Al2O3 particles was studied and the mean roughnesses (Ra), of the grit-blasted surfaces were then measured. The results show that variations of working distance, air pressure and blasting time significantly affect the resultant surface roughness. The results also show that a 90 degrees blasting angle gives slightly higher Ra but a significantly higher amount of grit residue, in comparison with the results obtained for a blasting angle of 45 degrees. After grit blasting, the specimens were plasma spray coated with 80% ZrO2 - 20% Y2O3 powder. The adhesive strength of the coating to the substrate was then measured according to the ASTM C633 standard. The results show that for a certain base metal, the adhesive strength is directly related to the surface roughness and hardness of the base material. Copyright (C) 2010 John Wiley & Sons, Ltd.