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Phase Evolution During Crystallization of Amorphous Titanium Aluminide Thin Films: Effect Mn and Nb Additions

  • R. Banerjee (a1), S. Swaminathan (a1), R. Wheeler (a1) and H. L. Fraser (a1)


Thin films of Ti-aluminides have been sputter deposited using a binary γ-TiAl based target and a quaternary γ-TiAl based target containing alloying additions of Nb and Mn. The as-deposited binary film consisted of microcrystalline agglomerates of α-Ti(Al) embedded in an amorphous matrix whereas the as-deposited quaternary film was found to be amorphous. These films have been annealed in a furnace under a protective Ar atmosphere (referred to as ex situ annealing) as well as on a hot stage in a transmission electron microscope (TEM), referred to as in situ annealing, to study the crystallization behavior of these films and also the effect of Nb and Mn additions on the same. Ex situ annealing of both binary and quaternary films resulted in a nanocrystalline microstructure consisting of primarily γ-TiAl with a small amount of finely dispersed α2-Ti3Al. During in situ annealing of the binary film, at 753 K (stage temperature), growth of the α-Ti(Al) phase was observed together with crystallization of a second phase in relatively thicker regions of the specimen. The first crystalline phase to appear during in situ annealing of the quaternary film was a surface crystallized metastable tetragonal phase at 873 K. Prolonged annealing at the same temperature resulted in the transformation of the amorphous region between grains of the tetragonal phase into γ-TiAl. Formation of the tetragonal and intergranular γ-TiAl phases were also observed in the thin regions of the binary film when it was heated to 873 K.



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