Hot corrosion behavior of commercial alloys in thermal energy storage material of molten MgCl2/KCl/NaCl under inert atmosphere

Hot corrosion behavior of three commercial alloys (stainless steel SS 310, Incoloy 800 H, Hastelloy C-276) in molten MgCl2/NaCl/KCl (60/20/20 mol%) under inert atmosphere was investigated by immersion tests at 700 degrees C for 500 h. SS 310 exhibited the highest corrosion rate, while Hastelloy C-276 showed the best corrosion resistance. All the studied alloys could not meet the requirements for commercial application (i.e., corrosion rate < 10 mu m/year for 30 year's lifetime). Microstructural analysis on the exposed alloy specimens using SEM, EDX and XRD shows that Cr was dissolved preferentially than Fe and Ni to form a corrosion layer with a porous structure during the corrosion. Moreover, the corrosion products (e.g., MgO, MgCr2O4, etc.) precipitated on the surface of the exposed specimens, as well as in the pores of the Cr-depleted corrosion layer. For SS 310 containing 2 wt% Si, Si was also dissolved and corrosion products containing Si were observed in the pores of the corrosion layer. Based on these findings, an impurity-driven corrosion mechanism is proposed to describe the hot corrosion behavior of the studied alloys in molten MgCl2/NaCl/KCl under inert atmosphere, which could assist the development of corrosion mitigation technologies in future work.