Morphology of L10-TiAl(Ag) precipitation in Ag-modified L12–Al3Ti

Transmission electron microscopy (TEM) examinations of Ag-modified Al3Ti with an L12-ordered structure have revealed the precipitation of L10–TiAl upon aging after quenching from higher temperatures. TEM observations revealed that plate-like L10–TiAl precipitates lie on {001} planes of (Al,Ag)3Ti matrix in the short aging period and the habit plane changed from {001} to {hhl} after a long period aging or higher temperature aging and finally to {225} of the matrix lattice. A quantitative X-ray microanalysis for determining the chemical compositions of precipitate and matrix has been done by using an analytical electron microscope. The L12 phase field in the Ti–Al–Ag system is severely skewed with respect to the temperature axis and is restricted into a much smaller field at lower temperatures. The coherency stresses across the precipitate/matrix interface is considered to be the main factor controlling the precipitate morphology.