Effect of Thermal Aging on the Corrosion Behavior of Wrought and Welded Alloy 22

Alloy 22 (UNS N06022) is a candidate material for the external wall of the high level nuclear waste containers for the potential repository site at Yucca Mountain. In the mill-annealed (MA) condition, Alloy 22 is a single face centered cubic phase. When exposed to temperatures on the order of 600 C and above for times higher than 1 h, this alloy may develop secondary phases that are brittle and offer a lower corrosion resistance than the MA condition. The objective of this work was to age Alloy 22 at temperatures between 482 C and 800 C for times between 0.25 h and 3,000 h and to study the corrosion performance of the resulting material. Aging was carried out using wrought specimens as well as gas tungsten arc welded (GTAW) specimens. The corrosion performance was characterized using standard immersion tests in aggressive acidic solutions and electrochemical tests in multi-component solutions. Results show that, in general, in aggressive acidic solutions the corrosion rate increased as the aging temperature and aging time increased. However, in multi ionic environments that could be relevant to the potential Yucca Mountain site, the corrosion rate of aged material was the same as the corrosion rate of the MA material