Environment-Induced Degradation and Crack-Growth Studies of Candidate Target Materials: Annual Progress Report (May 2002 – May 2003)

As indicated in the original proposal, the primary objective of this task is to evaluate the effect of hydrogen on environment-assisted cracking of candidate target materials for applications in spallationneutron- target (SNT) systems such as accelerator production of tritium (APT) and accelerator transmutation of waste (ATW). The materials selected for evaluation and characterization are martensitic stainless steels including Alloy HT-9, Alloy EP 823 and Type 422 stainless steel. The susceptibility to stress corrosion cracking (SCC) and hydrogen embrittlement (HE) of these materials are being evaluated in aqueous environments of interest using tensile specimens under constant load and slow-strain-rate (SSR) conditions. Further, the localized corrosion behavior of these alloys is being evaluated by electrochemical polarization techniques. The extent and morphology of cracking and localized corrosion of the tested specimens are being determined by optical microscopy and scanning electron microscopy (SEM). The concentration of hydrogen resulting from cathodic charging will be analyzed by secondary ion mass spectrometry (SIMS). More recently, this experimental program has been refocused to evaluate the effect of molten LBE on the corrosion behavior of similar target materials in the presence of oxygen. Since the Materials Performance Laboratory (MPL) currently cannot accommodate this type of testing, the lead-bismuth-eutectic (LBE) loop at the Los Alamos National Laboratory (LANL) will be used to contain the stressed test specimens to evaluate the SCC, HE, and localized corrosion (pitting and crevice) behavior in the molten LBE environment. Since the magnitude of the applied load/stress during these tests cannot be monitored or controlled (as in conventional SCC/HE experiments) in the LBE environment, the test specimens will be self-loaded. Two types of specimen configurations, namely C-ring and U-bend, are being used to perform these desired experiments. The stress of principal interest in both types of specimen is the circumferential stress. SCC tests using these types of self-loaded specimens are also being performed in aqueous environments having neutral and acidic pH values at ambient and elevated temperatures