Figure 7. Body-centered binary intermetallics often show a structural transformation from a high-temperature, disordered body-centered cubic phase (top left, space group Im3m) to an ordered austenite phase with the CsCl structure (top right, space group Pm3m). At lower temperatures, a second phase transition takes place from an austenite structure to a twinned martensite phase, pictured here (bottom) as three variants of a body-centered tetragonal phase (space group P4/mmm, unique axis c indicated with arrows). Different domains in the material adopt these structure variants. When the domain walls move under applied stress, reversible strain is produced. Adapted from Ref 4. Used by permission. |
