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Title:
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Corrosion of stainless steel coatings applied by different thermal spray techniques
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Author(s):
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Published by:
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Publication date:
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ECN
Energy Efficiency in Industry
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1-10-1998
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ECN report number:
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Document type:
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ECN-RX--98-055
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Article (scientific)
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Number of pages:
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17
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Published in: Contribution to EuroCorr Conference, Utrecht, 38 September - 1 October 1998 (), , , Vol., p.-.
Abstract:
Stainless steel coatings of type AISI 316 were manufactured with arc wirespraying (AWS), atmospheric plasma spraying (APS) and high velocity oxygen
spraying (HVOF) on carbon steel substrates. The AWS coatings was the most
porous coating with poor cohesion between the solidified spray particles. The
WOF coating was dense with almost no oxide phase. 'Me plasma sprayed coating
was less porous than the AWS coating but contained almost the same amount of
oxides (1.4-5%). After electrochemical testing in 3% sodium chloride none of
the exposed overlayers revealed any form of corrosion. In contrast to the
HVOF sample the AWS samples, with poor cohesion between the splashes, showed
severe corrosion between coating and substrate interface. For an inert
overlayer the permeability, governed by the cohesion between the splashes,
determines corrosion protection of the substrates. After exposure to 0.5 M
sulphuric acid the AWS coating was corroded half way down the coating
thickness. The as-sprayed oxides were dissolved but also the metallic matrix
was corroded. Both the APS and the RVOF coatings showed minor attack close to
the surface. In the HVOF coating the splash boundaries were broadened
indicating crevice corrosion. The main corrosion mechanism in sulphuric acid
showed to be dissolution of the oxidic phase facilitated by the poor cohesion
in the thermal sprayed coatings. In absence of this species crevice corrosion
degrades the coating. 6 refs.
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