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  • Interfacial reactions and oxygen diffusion in thin ▫$TiO_2Al$▫ and ▫$TiO_2/Ti_3Al$▫ bilayers
    Van Lier, Jan ...
    Although Ti-Al alloys possess excellent mechanical properties, application of these materials at high temperatures is limited due to their poor oxidation behaviour: instead of closed, protective ... alumina layer, usually a mixture of titanium oxide and aluminium oxyde is formed. In order to controll the growth of oxyde scale, a detailed understanding of the oxidation process is required. Recent oxidation studies on [gama]-TiAl indicate the influence of the solid-solid reactions aat the metal/oxide interface on the constitution of the initial oxide layer. Investigations at Al[sub]2O[sub]3/Ti[sub]xAl[sub]y bilayers revealed dissolution of alumina, diffusion of oxygen into the metal layer and phase transformations. In this paper results on the thermal stability of TiO[sub]2/Ti[sub]3Al and TiO[sub]2/TiAl bilayers are presented. The bilayers (100 nm oxide/300 nm metal) were sputter deposited onto Si substrates covered with a 50 nm TiN buffer layer. The samples were heated under an Ar atmosphere applying a constant heaating rate of 40 K/min up to different maximum temperatures, followed by quenching down to room temperature with a roughly estimated cooling rate of 200 K/min. Concentration-depth profiles were determined using Auger electron spectroscopy in combination with ion sputtering and applying trget-factor analysis to distinguish between different states of chemical bonding. The microstructure was investigated by means of X-ray diffraction analysis and transmition electron microscopy. In both systems, TiO[sub]2/Ti[sub]3Al and TiO[sub]2/TiAl, disolution of titanium oxyde and associated oxygen diffusion into the metal layer occurs already below 773 K. The amount of diffused oxygen increases with increasing final temperature. Target-factor analysis revealed that oxygen is mainly dissolved in Ti[sub]3Al, wheras it is bonded to aluminium in TiAl. Consequently, different oxygen depth profiles were observed. Annealing of TiO[sub]2/TiAl bilayers up to 973 K causes a minimum in oxygen content near the interface, where oxygen is preferentially dissolved and not bounded to aluminium in the metal layer. This result may be explained by the formation of new phase at the interface during heat treatment. The influence of the microstructure on the interfacial reactions at the associated oxygen diffusion will be discussed.
    Vir: Abstracts (Str. 253)
    Vrsta gradiva - prispevek na konferenci ; neleposlovje za odrasle
    Leto - 1999
    Jezik - angleški
    COBISS.SI-ID - 42722

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