Phase Selection During Interdiffusion in Ti-Fe Multilayered Films
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PHASE SELECTION DURING INTERDIFFUSION IN TI-FE MULTILAYERED FILMS
Z.H.Yan, M.L.Trudeau and R.Schulz R.Bormann+, A.Van Neste# and J.O.Str3m-Olsen* Hydro-Quebec Research Institute, Varennes, P.Q., Canada, J3X 151 for Materials Research, GKSS-Research Center, D-2054 Geesthacht, Germany # Metallurgy Department, Laval University, P.Q., Canada, GIK 7P4 * Centre for the Physics of Materials, McGill University, 3600 University Street, Montreal, P.Q., Canada, H3A 2T8 + Institute
ABSTRACT The formation of the metastable bcc solid solution and the amorphous phase during interfacial reaction of elemental multilayers has been studied using X-ray diffraction. Different kinds of interfaces have been synthesized in order to investigate the influence of the interfacial structure on phase evolution during annealing. The amorphization is found to be dependent on the structure of the interface and the results are discussed in terms of the kinetics and thermodynamics of the Ti-Fe system which has been calculated by the CALPHAD method.
INTRODUCTION The formation of metastable phases in the Ti-Fe system has been extensively studied by various methods: vapor quenching (1), mechanical alloying (2,3), ion beam mixing of elemental multilayers (4) and ion implantation of intermetallics (5). Most interests originate from the potential application of the Ti-Fe alloys for hydrogen storage (6,7) and magnetic recording (8). Although this system exhibits two intermetallic compounds, it doesn't show a large negative heat of mixing and has a stable bcc solid solution over a wide range of concentration at high temperature (9) implying comparable free energies between the disordered bcc solid solution and the amorphous phase at low temperature. Therefore it is expected that, in the Ti-Fe system, the solid state amorphization of multilayered films may critically depend on the interfacial structure. Since the discovery of amorphization by solid state reaction (10), the kinetics involved in the process has been of significant interest. It was reported for Ni-Zr, that the amorphization during solid state reaction depends on the defects at the interface, e.g., grain boundaries (11). The impurities were also found to play an important role in the process (12). These factors suggest the importance of nucleation for the formation of the amorphous phase. With less negative heat of mixing, generally speaking, the nucleation will play an even more important role in the amorphization process. Indeed, amorphous phase formation in Ti-Fe was found to be critically dependent on experimental conditions, such as oxygen content or milling intensity (2,6). These observations indicate a strong competition between the amorphization and the formation of the crystalline phases, as already suggested by the thermodynamics of the system. Therefore, the nucleation of the phases in the Ti-Fe system may be strongly influenced by the structure of the interfaces between Ti and Fe. It is the purpose of this paper to study the formation of metastable phase for different evaporation
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