Microstructure in a cubic to orthorhombic transition

Microstructures for a cubic to orthorhombic transition are constructed usin g a geometrically nonlinear, thermoelastic theory of martensitic transforma tions. Such microstructures are of interest because they provide low energy paths along which a specimen can transform. The particular microstructures considered are the twinned martensite, austenite-martensite, wedge, triang le, and diamond. More specifically, all possible twins are found along with the corresponding twinning elements and magnitude of the twin shear. Furth er, two kinds of austenite-martensite microstructures are studied: those wi th a single variant of martensite and those with twinned martensite. The re gions in the space of transformation stretches in which each of these micro structures exist are determined, and the shape strains and habit plane norm als are found as well. In addition, special microstructures, the wedge, tri angle, and diamond, are constructed with both the austenite-single variant and austenite-twinned martensite microstructures. These special microstruct ures are of interest because they provide a mechanism through which the tra nsformation may proceed more easily, and they are possible only in alloys w ith particular transformation stretches. Numerically computed level curves in the space of the stretches are presented on which the special microstruc tures are possible. These results may be useful in providing guidelines for alloy design.