Dislocation Substructure vs Transgranular Stress Corrosion Susceptibility Of Single Phase Alloys

The microstructure of deformed alloys which are susceptible to stress corrosion cracking has been investigated by transmission electron microscopy. It is found that the mode of failure is strongly related to the dislocation distribution. Alloys with a cellular arrangement of dislocation tangles have superior resistance to transgranular failure, whereas alloys containing planar groups of dislocations are generally more susceptible. In alloys, the active path for preferential electrochemical attack during transgranular stress corrosion cracking is associated with a continuous plane of disordered material which is created by the motion of dislocations through a matrix of short-range order. In superlattices, it is proposed that the active site for chemical attack is the antiphase boundary created during deformation by the accidental separation of superlattice dislocation pairs. The susceptibility of annealed, fully ordered single crystals to chemical embrittlement is predicted to depend on the continuity of the grown-in antiphase boundary structure.