Investigation on the Corrosion Behavior of Nickel-Base Alloys in Molten Chlorides for Sensible Heat Energy Applications

Nine selected alloys are exposed in molten KCl-LiCl (eutectic composition) at 1073 K for 167 h under argon atmosphere to predict the long-term corrosion behavior of these structural materials. The corrosive attack of each alloy is assessed with gravimetric methods, scanning electron microscopy, and energy-dispersive X-ray spectroscopy measurements. The corrosion rate of each alloy is calculated in accordance with ASTM G1-03. Low chromium containing alloys as HAYNES 242, Hastelloy B-3, and Hastelloy N revealed minor or no significant corrosive attack after molten chloride exposure. Alloy 600, Alloy 617, HAYNES 625, Hastelloy X, HAYNES 230, and HAYNES 188 with a chromium content w(Cr) > 8% show severe corrosive attack with complete chromium depletion along the near-surface layer and partially along grain boundaries. The results show that chromium forms chromium oxide with impurities of oxygen and water vapor at low oxygen partial pressures. This initiates an accelerated corrosion of the alloying elements in the matrix of Ni, Cr, Mo, Fe, and Co, due to chlorine formation. The influence of the composition of nickel-base alloys on the corrosion resistance is discussed based on the comparison of the gravimetric measurements and thermodynamic calculations.