Microstructural effects and mechanism of bcc-hcp-bcc transformations in polycrystalline iron
Résumé
Cycling the α↔ε transformation in polycrystalline Fe is investigated using in situ x-ray diffraction under quasihydrostatic conditions. The forward α→ε transformation starts at 14±1 GPa and completes at 18±1 GPa while the reverse ε→α transformation starts at 10.5±0.5 GPa and completes at 6±1 GPa. The anomalous evolution of c/a ratios of ε-Fe measured at the onset of the α→ε transition in earlier studies is not observed. Microstructural features are consistent with a Burgers path for the transformation. The forward α→ε transformation is sensitive to the average and intergranular stresses, inducing a strong variant selection with the c axes of the new ε phase preferentially aligned perpendicular to compression and concentrated into one single orientation. Partial texture memory is observed as the sample returns to the α phase but, as transformation cycles go on, irreversible changes occur in the microstructures that are later fully induced by the cycles of phase transformations.
Domaines
Chimie Matériaux Physique [physics] Matière Condensée [cond-mat] Science des matériaux [cond-mat.mtrl-sci] Physique [physics] Physique [physics] Géophysique [physics.geo-ph] Physique [physics] Astrophysique [astro-ph] Planète et Univers [physics] Astrophysique [astro-ph] Planète et Univers [physics] Sciences de la Terre
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