The role of texture in stress-corrosion cracking of metals and alloys

The possible role of texture in transgranular stress-corrosion cracking is considered by application of the Stress-Assisted Directed Dissolution (SADD) model, which accounts for the observed predominance of particular crystallographic fracture planes in face-centered cubic metals and alloys. The model postulates that cleavage-like cracks may initiate directly from the free surface along {111} "slip-plane dissolution" (SPD) slots or by grain-boundary corrosion slots. Continued transgranular growth may occur by transition to other low-index planes, e.g., {110}, {001}, etc., dependent on the orientation and growth direction of the initiating cracks with respect to the applied load. Effective growth-rates can vary with fracture plane and growth direction. The mechanism for these possible transitions involves enhanced dissolution due to the large elastic strain-energy existing in the near crack-tip region of the elastic-plastic domain. The possible favored transitions are determined by the elastic stress distribution in front of the growing slot (or grain boundary) and the degree of relaxation due to dislocation-emission from an initiating {111} slot. Calculations show a strong preference for transition to {110} fracture planes or continued growth of the {111} initiating cracks, which, with increased crack-tip stress-concentration, occurs independent of dislocation core energy but wholly dependent on SADD. Comparison with available experimental results indicates that anisotropic bonding may also influence the observed preference for {110} fracture. The practical application of these results to polycrystaline materials would require textures, whereby the orientation of initiating grain-boundary or {111} SPD cracks and subsequent transition cracks are such as to minimize initiation and growth of transgranular cracks.