A critique on some of the concepts regarding planar faults in crystals

The construction of the γ surface requires the application of mechanical constraints in order that the energy of non-equilibrium fault configurations can be calculated. The choice of mechanical constraints is not unique and it is shown that γ surfaces constructed using different schemes can differ significantly. The measurement of planar fault energies using transmission electron microscopy techniques is also critically assessed. It is discovered that the constraining effects of the bounding partial dislocations can significantly modify the local fault energy. Experimentally measured fault energies should therefore be expected to differ from atomistically calculated values.