High-temperature corrosion rate and diffusion modelling of Ni-coated incoloy 800H alloy in MgCl2–KCl heat transfer fluid

Abstract

The polarization and long-term dipping corrosion behaviors of pristine and Ni-coated Incoloy 800H (800H) alloys were investigated in the eutectic MgCl 2 –KCl molten salt at different temperatures and compared their performance with expensive Haynes 230 (H230) alloy. The corrosion rates of all the studied alloys increased with temperature. The corrosion rates obtained from the electrochemical study showed Ni-coating increases the corrosion resistance of 800H alloy. Further, the linear polarization measurements were also performed at different temperatures to investigate the effect of Ni-coating on the exchange-current density. A long-term corrosion study showed that 800H has a higher corrosion rate than H230. However, Ni-coating significantly decreased the corrosion rate of 800H (even lower than H230) in the molten MgCl 2 –KCl salt. A diffusion model for Ni-coated 800H was presented to describe the diffusion behavior of Cr, Fe, and Ni elements in the Ni-coated 800H alloy in a long-term corrosion study. The diffusion model was simulated based on the partial differential equations and known initial boundary conditions. The simulated result is compared with experimental data by altering the diffusion coefficient and reasonable values of diffusion coefficients of Cr, Fe, and Ni in 800H alloy and Ni-coating. The estimated diffusion coefficient (D) values in the Ni-coating from 800H alloy are in the range of 2–4 × 10 −11 cm 2 s ˗1 , 4–6 × 10 −11 cm 2 s ˗1 , and 5–8 × 10 −11 cm 2 s ˗1 for Cr, Fe, and Ni, respectively. The overall results indicated that Ni-coated 800H could be employed as a suitable alternative construction material for solar thermal energy storage containers. • We report polarization and long-term dipping corrosion of pure and Ni-coated Incoloy 800H alloy in MgCl 2 -KCl molten salt. • Measured corrosion rates and weight loss showed Ni-coating on Incoloy 800H substantially increased the corrosion resistance. • Exchange current densities of Incoloy 800H with and without Ni-coating were investigated at different temperatures. • A diffusion model of Fe and Cr elements in Ni-coated 800H alloy was validated experimentally.