Crystallography and morphology of D0(23)Al(11)Ti(5) precipitation in Ag-modified Ll(2)-Al3Ti

A detailed transmission electron microscopy (TEM) study has been made of th e crystallographic characteristics of precipitation of D0(23)-Al11Ti5 in Ag -modified Al3Ti with an L1(2)-ordered structure. TEM observations revealed that plate-like D0(23)-Al11Ti5 precipitates form multi-domain structures wh ich can be considered as a twin related structures with the tetragonal axis of twin I parallel to [100] direction and that of twin II parallel to [010 ] direction of the matrix. The particular habit plane, orientation relation ship and twin plane variants were carefully determined. A quantitative X-ra y microanalysis for determining the chemical compositions of the precipitat e and matrix has been done by using an analytical electron microscope. It i s found that these crystallographic and morphological features can be expla ined excellently by adopting the linear elastic theory developed primarily by Khachaturyan. The coherency stresses across the precipitate/matrix inter face is considered to be the main factor controlling the precipitate morpho logy. (C) 2000 Elsevier Science Ltd. All rights reserved.