Corrosion behavior of HVOF coated sheets |
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Authors: | B S Yilbas B J Abdul-Aleem M Khalid |
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Affiliation: | (1) Mechanical Engineering Department, KFUPM, Dhahran, Saudi Arabia;(2) Chemistry Department, KFUPM, Dhahran, Saudi Arabia |
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Abstract: | High velocity oxygen-fuel (HVOF) thermal spray coating finds application in industry due to its superior resistance to corrosion
and thermal loading. In the HVOF process, the metallic powders at elevated temperature are sprayed at supersonic speed onto
a substrate material. The powder granules sprayed impact onto each other, forming a mechanical bonding across the coating
layer. In most of the cases, the distances among the particles (powder granules sprayed) are not the same, which in turn results
in inhomogeneous structure across the coating layer. Moreover, the rate of oxidation of the powder granules during the spraying
process varies. Consequently, the electrochemical response of the coating layer surfaces next to the base material and free
to atmosphere differs. In the current study, the electrochemical response of a coating sheet formed during HVOF thermal spraying
was investigated. NiCrMoNb alloy (similar to Inconel 625) wass used for the powder granules. Thermal spraying was carried
out onto a smooth surface of stainless steel workpiece (without grid blasting), and later the coating layer was removed from
the surface to obtain the coating sheet for the electrochemical tests. It was found that the corrosion rate of the smooth
surface (surface next to the stainless steel surface before its removal) is considerably larger than that corresponding to
the rough surface (free surface) of the coating sheet, and no specific patterns were observed for the pit sites. |
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Keywords: | HVOF coating corrosion properties |
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