STRUCTURE AND CRYSTALLIZATION OF Fe-Si AMORPHOUS THIN FILMS

L'état amorphe et le processus de cristallisation de film amorphe de Fe-Si obtenus par évaporation sous vide ont été étudiés par spectroscopie Mössbauer, microscopie et diffraction électronique. Des spectres Mössbauer correspondant aux alliages amorphes ferromagnétiques Fe50Si50 et paramagnétique Fe30Si70 ont été obtenus par la technique en retour utilisant les électrons de conversion. Le large sextuplet obtenu à partir de Fe50Si50 comporte une structure fine qui ne peut être due à aucun composé connu ; ceci suggère l'existence d'un ordre à courte distance dans les alliages fraîchement préparés. Par recuit, il apparaît des modifications de cet ordre à courte distance, bien avant la cristallisation qui a lieu à 250°C, avec d'abord l'apparition du sextuplet caractéristique de Fe3Six suivi d'une composante de fer pure. Le recuit de l'alliage paramagnétique amorphe Fe30Si70 conduit progressivement à des cristaux de β-FeSi2 de plus en plus parfaits.Amorphous state and crystallization process of vacuum evaporated thin films of Fe-Si alloys were studied by means of Mössbauer spectroscopy, electron microscopy and electron diffraction. Mössbauer spectra from ferromagnetic amorphous Fe50Si50 and paramagnetic amorphous Fe30Si70 films were obtained with the back scattering method using the conversion electrons. In the typical broad sextet pattern from the Fe50Si50 film, a fine structure, which could not be attributed to any known chemical compounds or pure iron component, was observed, suggesting the existence of certain short range atomic configurations in the as deposited film. On the annealing, the change of shart range order preceded the amorphous-crystalline transformation which took place at around 250°C. By further annealing, Fe3Si sextets first appeared. It was then followed by the appearance of pure iron component that was one of the final products in the crystallization process. On the annealing of paramagnetic amorphous Fe30Si70, β-FeSi2 compound with defective structure was formed, and it gradually became a nearby perfect β-FeSi2 crystals by further annealings

PHASE ANALYSIS IN METALS AND ALLOYS BY MÖSSBAUER SPECTROSCOPY

Des limites de solubilité ont été calculées pour les très petites concentrations par une méthode numérique de simulation fondée sur les intégrales de transmission. A partir des résultats obtenus pour la solubilité du fer dans le titane et dans l'aluminium des paramètres thermodynamiques ont été calculés.A numerical simulation method using transmission integrals has been applied in the determination of phase boundaries in extremly small concentration ranges. From experimental results of Ti-dilute-Fe and Al-dilute-Fe alloys the solid solubilities and thermodynamical parameters were deduced

MARTENSITE TRANSFORMATIONS AND RELATED PROPERTIES OF MARMEM ALLOY RIBBONS PREPARED BY THE SPINNING ROLL METHOD

The melt spinning technique has been employed to refine the grain sizes of shape memory (marmem) alloys of Cu-Sn, Cu-Al-Ni, Cu-Zn, Cu-Zn-Al, Cu-Zn-Si and Ti-Ni. Ribbons 1-2 mm wide and 30-60 µm thick with grain sizes of up to 20 µm were obtained. Their martensite transformations and mechanical properties were investigated by optical and electron microscopy, X-ray diffractometry, electrical resistance measurements and mechanical tensile tests. Cu-Sn and Cu-Al-Ni ribbons exhibited the best shape memory effect, while Cu-Zn alloys gave different properties from specimen to specimen, because of variable alloy concentration due to vaporization loss of Zn. Good shape memory ribbons have not yet been prepared in Ti-Ni