Study of Bonding Strength of Plasma-Sprayed Ti-Al Coating on Mild Steel Substrate

The effect of the surface roughness of a mild steel substrate on the adhesive strength of a plasma-sprayed Ti-Al coating was examined. The substrate surface was prepared by grit blasting or mirror polishing, and the bonding mechanism between the coating and the substrate is discussed. The adhesive strength of the Ti-Al coatings varied from 55 to 60 MPa with changes in the roughness from 1.2 to 7.5 mu m. The adhesive strength of the Ti-Al coating sprayed onto a mirror-polished substrate was 25 MPa. The adhesive strength of a sprayed Ti coating was also affected by the roughness, but that of a sprayed Al coating was not. The bonding mechanism should be a combination of the mechanical anchoring of the Ti compound phase in the coating and the metallurgical bonding of the Al phase to the mild steel substrate.