Unstable stacking fault energy

To understand ductile-to-brittle transitions, the Rice criterion in which the ratio between the surface energy (Griffith fracture energy) and the unstable stacking fault energy is often... 

Fig. 12(a) further shows that the 110 unstable stacking-fault energy is systematically smaller than the 211 fault energy for all pressures up to 400 GPa in Ta and Mo, and up to 230 GPa in V. This has important implications for the motion of a/2 < 111 > screw dislocations on 110 and 211 slip planes. At all... 

Fig. 12. Unstable stacking-fault energies for Ta, Mo, and V, as calculated with the MGPT method, (a) Energies y and for the 110) and 211) y surfaces, respectively and (b) scaled energy...

In particular, the scaled unstable stacking-fault energy is nearly constant as a function of pressure in the case of Mo, but clearly decreases with pressure for Ta and V. 

At lower temperatures, the y-phase in the 18Cr-10Ni-Ti steel is unstable. This is indicated by a decrease in the stacking fault energy at low temperatures In this material at low temperatures, the e-phase forms during thermal cycling and the a-phase forms under loading. 

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