RETRACTED: Microstructure of carbide precipitates in L12-Ni3Al and L10-TiAl (Retracted article. See vol. 21, pg. 609, 2015)

The crystallographic structures of carbide formed in Ni3Al- and TiAl-based intermetallics containing carbon are investigated in this study using transmission electron microscopy. In an Ll(2)-ordered Ni3Al alloy with 4 mol.% of chromium and 0.2 mol.% to 3.0 mol.% of carbon, fine octahedral precipitates Of M23C6 type carbide were formed in the matrix by aging at temperatures around 973 K after solution annealing at 1423 K. TEM examination revealed that the M23C6 phase and the matrix lattices have a cube-cube orientation relationship and maintain partial atomic matching at the {111} interface. After prolonged aging or by aging at higher temperatures, the M23C6 precipitates adopt a rod-like morphology elongated parallel to the < 100 > directions. In L1(0)-ordered TiAl containing from 0.1 mol.% to 2.0 mol.% carbon, TEM observations reveal that needle-like precipitates, which lie only in one direction parallel to the [001] axis of the L1(0) matrix, appear in the matrix mainly at dislocations. Selected-area electron diffraction (SAED) patterns analyses showed that the needle-shaped precipitate is perovskite-type Ti3AlC. The orientation relationship between the Ti3AlC and the L1(0) matrix was found to be (001)(Ti3AlC)//(001)(L10) (matrix) and [010](Ti3AlC)//[010](L10) (mwix). By aging at higher temperatures or for a longer period at 1073 K, plate-like precipitates of TiAIC with a hexagonal structure form on the {111} planes of the L1(0) matrix. The orientation relationship between the Ti2AlC and the L1(0) matrix is (0001)(Ti2AlC)//(111)(L10) (matrix) and (Ti2AlC/L10 matrix).