Mh. Staia et al., Effect of substrate roughness induced by grit blasting upon adhesion of WC-17% Co thermal sprayed coatings, THIN SOL FI, 377, 2000, pp. 657-664
WC-Co thermally sprayed coatings are often used for their high hardness and
resistance to abrasion and erosion-induced wear. Several compositions rang
ing mostly from 12 to 18% Co are commercially available and numerous studie
s have reported the changes in hardness and wear properties in relation to
these compositions. A great number of parameters influence functional as we
ll as adhesive properties of thermally sprayed coatings. Among them the pre
paration of the substrate by grit blasting before spraying is of first impo
rtance. The grit blasting generates sufficient surface roughness, which ens
ures mechanical anchoring between the coating and the substrate. By varying
the grit blasting pressure between 0.345 and 0.621 MPa, an average surface
roughness ranging from 9.74 to 12.57 mum was obtained. It was shown that a
dhesive properties of WC-Co coatings, as measured by both interfacial inden
tation and by using the pull-off test (ASTM standard C633-79), are positive
ly affected by roughness variations. Image analysis of the fracture surface
s upon tensile test was proven to be an excellent tool for determining the
extent of the adhesive and cohesive failures. The influence of substrate ha
rdening, due to the grit blasting, and heat treatment of the coatings is as
sessed in relation to the adhesion results. It is shown that the influence
of coating thickness on the adhesion strength was eliminated for samples wh
ich were grit-blasted at pressures of 0.483 and 0.621 MPa and, subsequently
, heat treated. However, when the grit blasting pressure of 0.345 MPa was u
sed, different values for adhesion strength were determined to be a functio
n of the coating thickness, indicating that the heat treatment has not been
able to completely eliminate the existing residual stresses of the coating
s. (C) 2000 Published by Elsevier Science B.V. All rights reserved.