Investigation of the nucleation and growth behavior of Ti2AlC and Ti3AlC nano-precipitates in TiAl alloys

In this work, the nucleation and growth behavior of Ti2AlC and Ti3AlC nano-precipitates in Ti–44Al–1.2C alloys were systematically studied by observing their distribution, morphology, and interface atomic structure. The experiment results show that the needle-like C atom segregation zones in TiAl alloys are the nucleation site of Ti2AlC, and the long axis direction of segregation zones is parallel to the TiAl(111) plane. The rod-like Ti2AlC nano-precipitates mainly distribute at the TiAl/Ti3Al interface, and the orientation relationship between them is [1̅01\bar{1}01]TiAl//[112̅011\bar{2}0]Ti2AlC//[112̅011\bar{2}0]Ti3Al, (111)TiAl//(0001)Ti2AlC//(0001)Ti3Al. The needle-like Ti3AlC nano-precipitates distribute in TiAl with the orientation relationship of [001]Ti3AlC//[001]TiAl, (100)Ti3AlC//(100)TiAl, (020)Ti3AlC//(020)TiAl, and (110)Ti3AlC//(110)TiAl during the nucleation stage. After growing into the rod-like, the orientation relationship between Ti3AlC precipitates and TiAl is [11̅01\bar{1}0]Ti3AlC//[11̅01\bar{1}0]TiAl, (001)Ti3AlC//(001)TiAl, (220)Ti3AlC//(220)TiAl, and (111)Ti3AlC//(111)TiAl. Both the needle- and rod-like Ti3AlC precipitates preferentially grow along the [001]TiAl direction. The crystal structure and lattice mismatch between Ti2AlC and Ti3AlC nano-precipitates and the TiAl matrix determine their distribution, morphology, and interface atomic structure.