A necessary criterion for brittle fracture in crystals is established, in terms of the spontaneous emission of dislocations from an atomically sharp cleavage crack. We have calculated the stability of a sharp crack against emission of a blunting dislocation for a number of crystals and crystal types in two dimensions and the energy to form a stable loop of dislocation from the crack tip in three dimensions. We find that contrary to previous expectations, an atomically sharp cleavage crack is stable in a wide range of crystal types, but that in the face centred cubic metals investigated, blunting reactions occur spontaneously. Of the body centred metals investigated, iron is an intermediate case between the brittle and ductile cases, and the ionic and covalent crystals investigated are all stable against dislocation emission. Qualitatively, we find that crystals whose dislocations have wide cores, and small values of the parameter μb/γ (μb/γ⋦7·5 to 10) are ductile while crystals with narrow cores ...

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Ductile versus brittle behaviour of crystals

A review of conduction phenomena in Li-ion batteries

http://myweb.clemson.edu/~daw/D_reprints/MatSciRep.v9p251y93.pdf

The embedded-atom method: a review of theory and applications

Mixed ionic-electronic conducting (MIEC) ceramic-based membranes for oxygen separation

We discuss theoretical models of interfacial embrittlement by solute segregation. Of properties susceptible to alteration by segregation, the ideal work of interfacial separation, 2 γ int , is predicted to have an important but probably not exclusive role in controlling embrittlement. A thermodynamic framework for estimating 2 γ int from data available through free surface and grain boundary adsorption studies is outlined, and relevant segregation energies are given for carbon, phosphorus, tin, antimony and sulphur segregation in iron. Data from intergranular fracture experiments involving these same segregants is also summarized in an attempt to test the idea that segregation-induced embrittlement (or ductilization) can be understood in terms of the segregant's effect on 2 γ int . Uncertainties in present data do not allow a convincing test, but it is not implausible that the deleterious effects of phosphorus, tin, and sulphur in iron can be understood in this way. The effect of carbon does not seem to be similarly understandable, although that may be due to the inappropriateness of the only available surface segregation data in that case, which are for a (001) surface rather than a general polycrystalline surface created by intergranular fracture.

D. McLean

Papers

Grain boundaries in metals