DEBYE-WALLER FACTORS AND SUB-LATTICE ORDERING IN TiAl. S. Swaminathan, S. Jayanti, I. P. Jones^*, D. M. Maher^**, A. W. Johnson^***, H. L. Fraser, Dept. of Matls. Sci. and Eng., The Ohio State University, OH, ^*School of Metallurgy and Materials, University of Birmingham, UK, ^**Dept. of Matls. Sci. and Eng., North Carolina State University, NC, ^***Center for Microscopy, University of Western Australia, Australia.

The Debye-Waller factors of Ti and Al sites of Ti-⁵⁴Al alloy have been determined by four circle single crystal x-ray diffraction method. The analysis of x-ray diffraction data shows an ordered substitution of excess Al atoms (i.e. those over the stoichiometric composition) on the Ti sites. For the off-stoichiometric alloy studied, the least squares analysis yielded unequal Debye-Waller factors for the two crystallographically equivalent sites on the Ti-sublattice. This result is consistent with the ordering of excess Al atoms on Ti sites. On going research plan involves, data collection and analysis of x-ray diffraction intensities from a series of TiAl single crystals of different compositions. The results of this work and the effect of sublattice ordering on structure factors measured by convergent beam electron diffraction method will be presented.