Computer Simulation of Twin Formation during the Displacive c→t′ Phase Transformation in the Zirconia‐Yttria System

The kinetics of the displacive cubic‐to‐tetragonal (c→t′) phase transformation and the evolution of twin structure of Y₂O₃‐ZrO₂ systems were investigated by employing the time‐dependent Ginzburg‐Landau equations, in which the displacive modes were described by nonconserved order parameters. The original elasticity theory of Khachaturyan, in a sharp‐interface description for an arbitrary distribution of second‐phase precipitates in a matrix, was reformulated in the spirit of the diffuse interface theory of Cahn and Hilliard for interphase boundaries. The influence of thermodynamic conditions, clamped or stress‐free, on microstructure evolution was studied. Our computer simulation showed that, even though the thermodynamic equilibrium is the single domain under a stress‐free condition, the twin structure can form during a kinetic path of the phase transformation, and it is the clamped condition which results in the formation of stable twins.