Some observations on the stress-corrosion cracking of α-brass and similar alloys

An attempt has been made to establish a mechanism for stress corrosion by direct observation on the propagation of cracks in α-brass tested under ammonia. The observations indicate that failure might be described by a two-stage process, of local embrittlement, followed by a cleavage-like fracture. Such a model demands that the embrittled zone should have its mechanical properties modified in such a way as to allow a crack to form and reach some critical velocity, whilst the normal unattacked metal should be able to support this free-running crack for extensive failure to occur. These requirements are examined in the light of current ideas on the metal physics of fracture.