Abstract: The microstructures of Cr modified Al3 Ti containing Al2 Ti and L10-AlTi precipitateshave been investigated in terms of transmission electron microscopy ( TEM). Fine pre-cipitation of Al2 Ti (Ga2Hf type structure) and L 1o-AlTi(Cr) occurs in L l2-Al3 Ti(Cr)by aging around 973K. The aging behavior was investigated by microhardness mea-surements. TEM observations revealed that plate-like Al2 Ti precipitates lie on { 100}planes of the L12-Al3 Ti(Cr) matrix with the c axis of the tetragonal phase perpendic-ular to the thin plate. As contrast with Al2 Ti precipitates, L1o-AlTi(Cr) precipitatesform thin plate and lie on {100} planes of L12-Al3Ti(Cr) matrix at the initial agingtime and for long time aging the habit plane of the thin plate deviated from {100}plane and finally formed a kinked plate. The coherency stresses across the precipi-tate/matrix interface are considered to be the main factor controlling the precipitatemorphology.``

Key words: titanium aluminide, based on Al3 Ti, age-hardening, mechanical property, precipitate