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Home  >  Journal list  >  MATERIALS TRANSACTIONS  >  Vol.43  No.11 (2002)  >  pp.2860-2865

MATERIALS TRANSACTIONS
<<Previous article Vol.43  No.11 (2002)   pp.2860 - 2865 Next article>>

Corrosion Behavior of Thermally Sprayed WC Coating in Na2SO4 Aqueous Solution

Mutsumi Takeda1), Naoki Morihiro1), Ryuichiro Ebara2), Yoshio Harada3), Rongguang Wang1) and Mitsuo Kido1)
1) Hiroshima Institute of Technology
2) Faculty of Engineering, Kagawa University
3) Tocalo Co., Ltd.


WC–Co thermally sprayed coating, formed by high velocity oxygen-fuel flame spraying, has had the problem of low corrosion resistance in aqueous solutions. Furthermore, much remains unknown regarding corrosion reactions on coating surfaces and the formation of passivation films. This study focused on changes of the corrosion surfaces of two thermally sprayed coatings, WC–12Co and WC–10Co–4Cr, with immersion time. The chemical composition of the corrosion surfaces was analyzed by electron spectroscopy, and the relation with passivation film stability is discussed. For WC–12Co, the thermally sprayed coating was immersed in Na2SO4 solution. The W and Co components were dissolved by extended anodic reaction. Oxides of W and Co were then formed on the surface of the thermally sprayed coating. However, these oxides appeared to have little effect on the corrosion. Passivation film, which mainly consists of Cr2O3, was formed on the surface of WC–10Co–4Cr thermally sprayed coating immediately after immersion, and limited the dissolving of coating components into the aqueous solution. However, it is suspected that this film did not completely cover the entire coating surface. It is probably a thin porous film formed as islands.


Keyword:
thermally sprayed coating, high velocity oxygen-fuel flame spray, tungsten carbide cermet coating, passivation film, immersion, corrosion resistance, anodic polarization

Received: May 23, 2002
Accepted: September 24, 2002 , Published online: September 06, 2005
Copyright (c) 2005 The Japan Institute of Metals

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