The formation of lamellar microstructures in a Ti-62 at.% Al alloy at tempe
ratures of 900-1100 degreesC was investigated by transmission electron micr
oscopy (TEM). The lamellar structure consists of gamma -TiAl + r-Al2Ti in t
he equilibrium state. h-Al2Ti and Al5Ti3 are observed in the as-cast alloy,
but Al5Ti3 transforms into gamma -TiAl above 900 C. The phase h-Al2Ti tran
sforms into r-Al2Ti by two alternative processes, i.e. by continuous or dis
continuous transformation. While the first process is comparably sluggish,
areas generated by the second process enlarge quickly. leading to the forma
tion of a fine lamellar microstructure of gamma -TiAl and r-Al2Ti. This fin
e lamellar microstructure coarsens through lamellar fault or/and grain boun
dary migration during long time annealing. In the equilibrium state, the fu
lly coarsened lamellar microstructure contains regular misfit dislocations.
i.e. two types of [110] edge dislocations in the (001) planes at the inter
lamellar boundaries. (C) 2001 Elsevier Science Ltd. All rights reserved.