The ideal Griffith energies and the critical stress intensity factors for three cleavage modes were determined from the calculated elastic constants and surface energies. The propensity for crack tip deformation was estimated on the basis of the calculated antiphase boundary, complex stacking fault and superlattice intrinsic stacking fault energies and the anisotropic coupling effect on dislocation mobility, i.e. non-Schmid effects. It was shown that while the calculated Griffith energy of Ni3 Si was larger than that of Ni3Al, dislocation emission from a crack tip was easier and dislocation mobility was higher in Ni3Al than in Ni3Si. When a crack was loaded in a mixed mode (KI + KIII), emission of a Shockley super-partial from the crack trailing extended superlattice intrinsic stacking fault was predicted and confirmed by in situ straining transmission electron microscopy observations of Ni3Al.

Crack-Tip Dislocations and Fracture Behavior in Ni3Al and Ni3Si. Yoo, M.H., Fu, C.L., Horton, J.A.: Materials Science and Engineering A, 1994, 176[1-2], 431-7