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Reconstructive and Displacive Transformations: Part IV

Part 4 in the story of displacive and reconstructive phase changes. Displacive transformations involve the coordinated movement of atoms. Such movements cannot be sustained against strong defects such as grain boundaries. This is why martensite or bainite plates are unable to cross grain boundaries. Less drastic defects such as isolated dislocations also hinder the progress of such transformations, but can often be incorporated into the martensite lattice. It is well established that when the strain in the austenite becomes sufficiently large, the motion of glissile interfaces becomes impossible, causing the transformation to halt. This applies to all cases involving the translation of glissile interfaces, whether their motion leads to a phase change, or simply to a reorientation of the lattice as in mechanical twinning. The phenomenon is known as mechanical stabilisation and is a sure way of distinguishing the displacive and reconstructive mechanisms of solid state transformations. More details on http://www.phase-trans.msm.cam.ac.uk/...