Cooperative Atomic Shear

Synchro shear (diffusionless cooperative atom movement) Fe and Cr doped gamma (3)... 

The basic PTMC presented above and the notion of an internally modulated martensite phase applies to all known martensitic transformations. The idea of a shape change and lattice (Bain) correspondence is also universal. We may, therefore, conclude that martensitic transformations are shear-like (displacive) in nature, involving cooperative atomic movements. There will, accordingly, by predictable interactions with mechanical stresses, as will be seen later. 

Consequently, the resistivity decrease (increase) within the temperature range, Ms - MS(MS - As), is simply interpreted as the decrease (increase) in the concentration of antiphase boundaries as the cooperative shear movements of atoms take place by way of shear vector, S2 (S3). This suggests that the total resistivity of TiNi(lI) is given by the resistivity curve above 125 °C. Similarly, the resistivity curve below the Ms temperature is the total resistivity of TiNi(III). By extrapolating the total resistivity of TiNi(II) and TiNi(III) as shown in Fig. 13 (dotted lines), the total resistivity of TiNi(II) is shown to be lower than that of TiNi(III) within the transition temperature range, Ms - As. In order to confirm this interpretation, it was logical to obtain other data corresponding to the two extreme resistivity curves, Fig. 12 (a) and (c). 

The cooperative movement of large numbers of atoms represents an alternative, and in some ways more precise [83], mechanism of reaction in addition to the well-established interface advance and diffusion-controlled processes which are considered throughout this book. Examination of the possible participation of crystallographic shear in the reactions of solids has been largely restricted to refractory oxides, but comparable or related behaviour could, in principle, operate in a variety of other solid state rate processes. 

Intermolecular Shear "Atoms" E, A and F cooperatively shear relative to atoms G, B, C and D. 

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