Non-affine fields in solid-solid transformations: the structure and   stability of a product droplet
  We describe the microstructure, shape and dynamics of growth of a droplet of martensite nucleating in a parent austenite during a solid-solid transformation, using a Landau theory written in terms of conventional affine, elastic deformations and {\em non-affine} degrees of freedom. Non-affineness, $\phi$, serves as a source of strain incompatibility and screens long-ranged elastic interactions. It is produced wherever the local stress exceeds a threshold and anneals diffusively thereafter. A description in terms of $\phi$ is inevitable when the separation between defect pairs, possibly generated during the course of the transformation, is small. Using a variational calculation, we find three types of stable solutions ({\hv I}, {\hv II} and {\hv III}) for the structure of the product droplet depending on the scaled mobilities of $\phi$ parallel and perpendicular to the parent-product interface and the stress threshold. In {\hv I}, $\phi$ is vanishingly small, {\hv II} involves large $\phi$ localized in regions of high stress within the parent-product interface and {\hv III} where $\phi$ completely wets the parent-product interface. While width $l$ and size $W$ of the twins follows $l\propto\sqrt{W}$ in solution {\hv I}, this relation does not hold for {\hv II} or {\hv III}. We obtain a dynamical phase diagram featuring these solutions and argue that they represent specific microstructures such as twinned or dislocated martensites. 
Arya Paul (SNBNCBS, Kolkata), Surajit Sengupta (IACS, Kolkata) and   Madan Rao (RRI & NCBS, Bangalore)
cond-mat.mtrl-sci