Predicted Habit Planes From Two Models: Invariant-Plane-Strain and Elastic-Energy-Minimization
H M. Ledbetter
We calculated habit planes (austenite-martensite interface planes) using two approaches: (1) the invariant-plane-strain (IPS) model proposed by Wechsler-Lieberman-Read and Bowles-Mackenzie and (2) elastic-strain-energy minimization (EEM) of a thin-disc inclusion using a model similar to those described by Eshelby, Mura, Khachaturyan, and others. We considered three example materials: In-Tl, Au-Cd, Fe-Ni. The IPS model requires as imput the austenite and martensite unit-cell dimensions and a plane of lattice-invariant shear. The EEM model requires cell dimensions and elastic-stiffness constants. (For the present EEM-model calculations, we neglected twinning.) In all three cases, the EEM model predicts habit planes on the (OK/) line and nears (011). This agrees well with the IPS-model prediction for the small-strain In-Tl case. For the moderate-strain Au-Cd case, the IPS-EEM disagreement is about 12 , the observed habit plane lying near the (hkk) line. The EEM model fails to predict the habit planes for large eigenstrain, large-twinning cases such as Fe-Ni, where the habit plane lies toward the unit-triangle center, away from any high-symmetry direction or zone.