Stress corrosion cracking of Ni-base and Ti alloys under controlled potential

摘要

Susceptibility to stress corrosion cracking (SCC) of alloy C-22 and Ti Gr-12, two211u001ecandidate alloys for the inner-container of the multi-barrier nuclear waste 211u001epackage, was evaluated by using the slow-strain-rate (SSR) test technique in a 211u001edeaerated acidic brine (pH (approx) 2.70) at 90 C. The strain rate used was 3.3 x 211u001e10(sup (minus)6) sec(sup (minus)1). Prior to being tested in the acidic brine, 211u001especimens of each alloy were pulled inside the test chamber in the dry condition 211u001eat room temperature (RT). Then specimens were exposed to the test solution while 211u001ebeing strained under different controlled electrochemical potentials. The 211u001emagnitude of the controlled potential was selected based on the corrosion 211u001epotential measured in the test solution prior to straining of the specimen. 211u001eResults indicate that, for Ti Gr-12, the times to failure were significantly 211u001eshorter compared to those for alloy C-22. Furthermore, Ti Gr-12 showed reduced 211u001eductility in terms of percent reduction in area and true fracture stress, as the 211u001econtrolled potential became more cathodic. Results also indicate that the time-to-211u001efailure and percent elongation reached the minimum values when Ti Gr-12 was 211u001etested under impressed potential of (minus)1162 mV. Finally, metallographic 211u001eexamination was performed to evaluate the primary fracture, and the secondary 211u001ecracking, if any, along the gage section of the broken tensile specimen.