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Abstract
The present study assessed the resistance against MD corrosion in a single-layer, oxide-forming NiCrAlSiTaY coating, and a double-layer NiCrAlSiTaY/laser-remelted (LRed) Al2O3 coating on an Inconel 625 (IN625) alloy. The NiCrAlSiTaY and Al2O3 coatings were applied onto the IN625 substrate using high velocity oxy-fuel spraying (HVOF) and air plasma spraying (APS) techniques, respectively. Coated and non-coated coupons were exposed, for 70 cycles, to a strong carburizing atmosphere of CO-50 % H2 in the temperature range of 550–750 °C to evaluate MD behavior. The results showed that the non-coated IN625 alloy contained a carbide free zone (CFZ), and secondary carbide precipitations of M23C6 and M6C and their subsequent in-situ oxidation were observed in the sub-surface layer. Such a development was indicative of the type III MD characteristic. The results also showed that the single-layer coating successfully protected the alloy, and only a part of the substrate underwent local oxidation. In addition, performing laser remelting (LR) on the Al2O3 coating significantly increased the resistance against the MD of the alloy through the removal of defects such as interconnected porosities, and via alumina phase transformation (γ → α). The lowest weight gain after 70 cycles of MD test was recorded for the double-layer coating coupons.
Published Version
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