Particular stacking fault energy

The four-body term is an application of exactly the ideas introduced in section 4.5.3 and culminating in eqn (4.95). Fig. 9.32 shows the relative contributions of different atoms in the faulted region to the overall fault energy. In particular, for a series of different metals the overall contribution to the stacking fault energy is decomposed layer by layer and each such contribution is itself decomposed into the relative contributions of the pair and four-body terms. 

The emergence of the types of polytypes described above may be rationalized on the basis of a variety of different ideas. Rather than exploring the phenomenon of polytypism in detail, we give a schematic indication of one approach that has been used and which is nearly identical in spirit to the effective Hamiltonian already introduced in the context of stacking fault energies (see eqn (9.18)). In particular, we make reference to the so-called ANNNI (axial next-nearest-neighbor Ising) model which has a Hamiltonian of the form... 

The interpretation of the behavior of Fe-Mn binary alloys containing 10 to 27% Mn requires an understanding of the behavior of the e-martensite phase. Despite recent informative research, particularly by Lysak and Nikolin ], the crystallography, formation kinetics, and mechanical behavior of the e-martensite phase are not fully resolved. The appearance of -martensite is associated with a low stacking fault energy of the austenite. Recent measurements (Fig. 3)... 

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. 

As we saw in Section 12.1, dislocations would always like to dissociate since this reduces the strain energy. Whether a particular dislocation will dissociate or not thus depends on the magnitude of the energy associated with the stacking fault. If the dislocation core spreads on the glide plane, it is glide dissociation otherwise it is at least partly climb dissociation. 

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