Transformation behaviour of a Ti50Ni47Fe3alloy. III. Martensitic transformation

Abstract In situ electron microscopic observations of the martensitic transformation and the martensite phase in a Ti50Ni47Fe3 alloy have indicated that the M8 temperature in thin foils of the subject alloy is about -98°C. The electrical resistance decreases abruptly at the M8 temperature. Below the M8 temperature, martensite plates nucleate and grow, and ‘consume’ the previously formed needle-like domains and their matrix. The crystal structure of the martensitie phase was determined to be of the B19′ type (monolinic). In addition to (IIT) internal transformation twins, stacking faults on the (001) basal plane and antiphase domains boundaries were observed within the martensite plates. The antiphase domains in the martensite, which are a consequence of atomic ordering rather than electronic ordering (charge density waves–CDWs), are different from those observed in the premartensitic phases. The ‘1/3’ superlattice reflections characteristic of CDW formation are not found in the martensitic phase. The rela...