Models film-induced cleavage

Film-induced cleavage models. It has been suggested that dealloying and/or vacancy injection could induce brittle fracture. The model assumes that a brittle crack initiates in a surface film or layer and this crosses the film/matrix without loss of speed. The brittle crack will continue in the ductile matrix until it eventually blunts and arrests. Verification of this model needs better understanding of the surface films and brittle fracture. (Jones)5... 

To explain the mechanism of transgranular S.C.C. in a brass, Newman and Sieradzki have proposed the film-induced cleavage model, according to which a brittle crack that initiates in a thin surface film propagates into the ductile matrix and eventually blunts and arrests, after which the process repeats itself [39, 44, 45]. 

SCC of iron or carbon steel under controlled potential conditions in conducting, high-temperature aqueous environments [29], where more than one mechanism may be operating, but the slip-dissolution and film-induced cleavage models are eminently testable using established methods with modem refinements. 

Later the lattice parameter was emphasized as a casual factor [143]. A detailed rationalization of see was made for iron exposed to anhydrous ammonia-methanol, where anodic oxidation of ammonia leads to interstitial penetration of nitrogen [69,100]. According to the film-induced cleavage model, such very thin, brittle layers are sufficient to allow cleavage through several pm of a body-centered cubic (bcc) material, whereas in fee systems a nanoporous metallic layer lO-lOOnm thick is a specific requirement as it is the only way of epitaxially coupling a brittle reaction product of sufficient thickness to the fee substrate. A special case may be the SCC of pure copper or silver, where a micropitted or tunneled zone is a possible brittle layer that could nucleate cracking [144,145]. 

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