NaCl-Induced High-Temperature Corrosion of Alloy 625 Fabricated by Laser Metal Deposition-Powder

Abstract

The present study describes the corrosion behavior of alloy 625 fabricated by laser metal deposition-powder in the presence of a solid NaCl deposit in laboratory air at 650 and 800 °C. The results showed that at both temperatures, the presence of the deposit had a catastrophic effect on the corrosion resistance of the alloy. The active corrosion mechanism resulted in a very thick and non-protective oxide scale and in a highly damaged metal zone beneath the oxide scale. Although the mechanism involved was the active corrosion mechanism at both 650 and 800 °C, differences were observed between these two temperatures. At 800 °C, the corrosion products were thicker, and the substrate was significantly more damaged, especially due to the formation of an interconnected network of voids. At 650 °C, the thick and continuous Cr₂O₃ layer, predominantly observed at 800 °C, was not present. The use of thermodynamic data helped to suggest possible explanations for the observed differences. Overall, the increase of temperature accelerated the degradation of the alloy and it was enhanced by a radical change of the main reactions of the active corrosion mechanism between 650 and 800 °C.