Critical Species in Stress Corrosion Phenomena

Abstract

Consideration has been given to the identification of the critical species in several stress corrosion systems. It is shown that in the α-brass/aqueous ammonia system, cupric complex ions of the type Cu(NH3)n2+ play a controlling role in the cracking process. Complex ions are also found to constitute the critical species in the embrittlement of silver chloride in certain aqueous environments. In the case of materials such as stainless steels and magnesium and aluminum alloys, which undergo stress corrosion cracking in chloride environments, the critical species may be the chloride ion itself or metal-chloride complexes. Attention is given to both the role of the critical species in the mechanisms of failure and the practical significance of these findings to stress corrosion testing. It is suggested that more attention to the chemistry of environments which cause stress corrosion cracking, with particular regard to the identification of the critical species, could be of significant practical value.