Corrosion behavior of 9Cr-ODS steel in stagnant liquid lithium and lead–lithium at 873 K

Corrosion experiments of 9Cr-ODS steel were carried out in static Li at 873 K for 250 h and compared with those of 9Cr-ODS in Pb–Li at the same exposure conditions. After exposure to liquid Li, 9Cr-ODS showed slight weight loss and decrease in hardness near surface. The tensile property exhibited a negligible change at 973 K and the creep property degraded at 973 K. By metallurgical analyses, 9Cr-ODS demonstrated a non-uniform corrosion behavior by preferential grain boundary attack and pronounced nodule-like morphology. The slight depletion of Cr was detected to about 15 μm in depth by chemical composition analyses. According to the calculation of free energy of formation, the nano-scale oxide particles of TiO2 in 9Cr-ODS were thermodynamically less stable while Y2O3 were more stable compared with those of Li2O in Li environment. However, Y2O3 may be reacted with Li to form YLiO2. The mechanism of corrosion was proposed as the slight dissolution of Cr and Fe in matrix into liquid Li, chemical interaction of nano-scale oxide particles with Li, preferential grain boundary attack and penetration of Li, and finally development of extreme nodule-like structure during cleaning of Li. On the contrary, 9Cr-ODS showed much larger weight loss and depletion of Cr near surface but less marked corroded morphology in Pb–Li than in Li, which may be derived from higher solubility of Cr and Fe and lower activity of Li in Pb–Li than in Li.