Protection of carbon steel against molten aluminum attack and high temperature corrosion using high velocity oxygen-fuel WC–Co coatings

Abstract

Cermet coatings of WC–17Co were thermally sprayed on carbon steel substrates with 0.4wt.% C using high velocity oxygen-fuel. The main goal of the investigation was the protection of carbon steel substrates against the attack in contact with molten aluminum using WC–Co coatings. Different spraying conditions were used and the optimal coating (226μm thickness) was characterized by SEM, XRD, Raman spectroscopy, micro-hardness tests and 3D optical profilometry in order to determine thickness, porosity, chemical composition, mechanical properties and surface roughness. Pull-off adhesion tests were conducted to evaluate the adhesion between coatings and substrate, and thermal cycling tests were also developed. The coated steel substrates were immersed in molten aluminum at different times (1, 2, 5 and 24h), and the resistance of the coatings to the attack of the molten aluminum alloy was studied. It was observed that the WC–Co was an effective physical barrier against molten aluminum penetration. Just after 2h of immersion, the uncoated carbon steel suffered aggressive attack by the liquid aluminum, which penetrated and cracked it. Conversely, the coated steel was unaffected after 24h of immersion due to the protection of the WC–Co coating, which suffered the liquid metal penetration only in the outer 35μm using 700°C as the higher temperature. The effectiveness of the WC–Co coating to protect carbon steel substrates against thermal fatigue deterioration and attack by molten aluminum was proved.