Environmentally Assisted Cracking of Nickel Strip in LiAlCl4 / SOCl2

Abstract

Constant extension rate tests (CERT) were used to evaluate the susceptibility of two cold‐rolled nickel strip materials to environmentally assisted cracking (EAC) in 1.5M . One strip material was made by a powder metallurgy (PM) process that started with carbonyl nickel. The other was cast and wrought (C&W). Both were 0.05 mm thick and cold‐rolled to the three‐quarter hard condition. The bulk impurity concentrations, grain structures, and mechanical properties of these two materials were similar. However, the C&W alloy was distinguished by a substantially higher bulk manganese content and oxygen‐rich inclusions, a large fraction of which also contained sulfur. EAC of the PM alloy, manifested principally as intergranular fracture, occurred in samples that were polarized to −50, 0, and +200 mV , but not in ones that were freely corroding at +3.65 V . These results are consistent with EAC being caused by a mechanism involving zero‐valent lithium, proposed by Scully et al1. In marked contrast to the PM alloy, the C&W alloy exhibited no susceptibility to Li‐assisted cracking. In ancillary experiments, performed with samples that were cathodically charged with hydrogen, only the PM alloy exhibited a high susceptibility to intergranular cracking. The present results indicate that subtle microstructural differences may affect the reliability of cells. Although the existing evidence is circumstantial, the results also suggest that lithium‐assisted and hydrogen‐assisted intergranular cracking have analogous sensitivities to grain boundary segregation of sulfur.