Corrosion behavior of 316SS and Ni-based alloys in a ternary NaCl-KCl-MgCl2 molten salt

This paper mainly investigated the corrosion of Fe-based 316SS and seven Ni-based alloys in molten NaCl-KCl-MgCl2 under N2 at 700 °C using static immersion experiment and microstructure observation. All alloys suffered the selective dissolution of Cr, resulting in the formation of subsurface voids. 316SS exhibited worse corrosion resistance than that of Ni-based alloys. Among Ni-based alloy, the corrosion resistance of alloys increased in the following order of Ni-Fe-Cr < Ni-W-Cr < Ni-Mo-Cr. The minor alloying elements such as Fe, Mo and W have also an obvious effect on the corrosion of alloys. Furthermore, Mo plays a better role in improving the corrosion resistance of Ni-based alloys than W due to the beneficial influence of Mo on preventing the outward diffusion of Cr from the alloys, in contrast to their calculated thermodynamical similarity. Otherwise, the morphology and composition of carbides on the alloy matrix have also an influence on corrosion of the alloys. The small continuous Mo-rich carbides on the grain boundaries tend to mitigate corrosion, while the large isolated W-rich carbides have no similar role.