Corrosion Resistance Enhancement of GH3625 Alloy Tube in High-Temperature KCl-MgCl2 Molten Salt Environment via Microstructure Tailoring

Abstract:

The effect of microstructure with different twin boundary fraction on the corrosion behavior of GH3625 alloy tube in high-temperature (600–800 ℃) KCl-MgCl₂ molten salt was investigated using EBSD, XRD, SEM, and EDS. The results show that with the increase in annealing temperature, the proportion of annealing twin boundaries in the equiaxed grains of GH3625 alloy tube is increased. Consequently, the higher the proportion of twin boundaries in the alloy at the same corrosion temperature, the better its high-temperature resistance to KCl-MgCl₂ molten salt corrosion. Furthermore, as the temperature increases, the corrosion resistance of a given set of samples to KCl-MgCl₂ molten salt deteriorates. In addition, at a constant grain size, an increased fraction of annealing twin boundaries correlates with enhanced corrosion resistance of GH3625 alloy tubes in KCl-MgCl₂ molten salt at high temperature. This is mainly attributed to the excellent intrinsic corrosion resistance of high-density stable annealing twin boundaries, coupled with the fact that the triple junction containing twin boundaries breaks the connectivity of the original high-angle grain boundary network, thereby suppressing the corrosion of the grain boundaries.