Dr. Yan et al., THE CORROSION BEHAVIOR OF A PLASMA SPRAYING AL2O3 CERAMIC COATING IN DILUTE HCL SOLUTION, Surface & coatings technology, 89(1-2), 1997, pp. 191-195
Al2O3 ceramic coatings plasma sprayed on the surface of metals change
greatly the corrosion law of metals in strong acid solutions and enhan
ce effectively their corrosion resistance property. In this paper, the
corrosion behaviour of a Q235 steel with plasma sprayed Al2O3 coating
s in a boiling 5% HCl solution is investigated. The corrosion rate of
the Al2O3 coating sprayed on the surface of Q235 steel is only 1/30 th
at of the 18-8 austenitic stainless steel under the same corrosion con
dition. However, the substrate and the Al2O3 ceramic coating itself ar
e also subjected to some corrosion because of pores and nonequilibrium
gamma-Al2O3 existing in the ceramic coating. The experimental results
demonstrate that at the early corrosion stage the corrosion mechanism
is channel corrosion with a large length to diameter ratio for the ch
annels; and the corrosion rate is controlled by the diffusion of corro
sion products in the channels; while at the late corrosion stage elect
rochemical corrosion occurs between the Ni-base alloy bond and the sub
strate. It was shown that channel corrosion can be restrained and the
substrate can be significantly protected by choosing a suitable alloyi
ng base layer, increasing appropriately the thickness of the coating,
and adopting a porous sealing treatment.