HIGH RESOLUTION ELECTRON MICROSCOPY STUDY ON OXIDEFILMS FORMED ON NICKEL-BASE ALLOYS X-750,182 AND82 IN SIMULATED HIGH FLOW VELOCITY BWR WATERCONDITIONS

摘要

This work contributes to characterization of the oxide films formed on nickel-base alloys (Alloy X-750, Alloy 82 and Alloy 182) under simulated BWR water environments at -10 or 18 m/s with or without iron injection. FIR SEM/TEM and FIB techniques were applied. The oxide thicknesses on different alloys were substantially different, ranging from 50 run to 8 μm. For Alloy X-750 and Alloy 182 exposed without iron injection, similar oxide phase compositions consisting of sub-micron Fe_2O_3 and NiFe_2O_4 grains as well as NiO were formed but with substantially different microstructures. For the corroded Alloy X-750 there was an additional dense layer of possibly Ni1.5Cro.5O3 in between the NiFe_2O_4 and NiO layers. On Alloy 82 which contained a relatively low Fe-content only a thin but dense film of Cr_(1.3)Fe_(0.7)O_3 was seen. With iron injection the oxide films formed on Alloy 82 were similar to that on the Alloy 182 without iron injection, suggesting that iron injection may play a similar role as if the alloy had an elevated iron content. The implication of the observations for material corrosion behavior in BWRs is elaborated.