The effect of carbon addition on the microstructures and mechanical properties of Ni3Al and TiAl intermetallic alloys were characterized. It was shown that carbon was not only an efficient solid solution strengthener in Ni3Al and TiAl, it was also an efficient precipitation strengthener by fine dispersion of carbide. Transmission electron microscope investigation was performed on the particle-dislocation interactions in Ni3Al and TiAl intermetallics containing various types of fine precipitates. In an L12-ordered Ni3Al alloy with 4mol% of chromium and 0.2-3.0mol% of carbon, fine octahedral precipitates of M23C6 type carbide, which has the cube-cube orientation relationship with the matrix, appear during aging. Typical Orowan loops were formed in Ni3Al containing fine dispersions of M23C6 particles. In the L10-ordered TiAl containing 0.1 to 2.0mol% carbon, TEM observations revealed that needle-like precipitates, which he only in one direction parallel to the [001] axis of the L10 matrix, appear in the matrix and preferentially at dislocations. Selected area electron diffraction patterns analyses showed that the needle-shaped precipitate was Ti3AlC of perovskite type. The orientation relationship between the Ti3AlC and the L10 matrix was found to be (001)Ti3AlC//(001)L10matrix and [010]Ti3AlC//[010]L10matrix. By aging at higher temperatures or for longer period at 1073K, plate-like precipitates of Ti2AlC with a hexagonal structure were formed on the {111} planes of the L10 matrix. The orientation relationship between the Ti2AlC and the L10 matrix was (0001)Ti2AlC//(111)L10matrix and [1120]Ti2AlC//[101]L10matrix. High temperature strength of TiAl increased appreciably by the precipitation of fine carbide. Dislocations bypassed the carbide needles at higher temperatures.

The Effect of Carbide Precipitation on the High Temperature Deformation of Ni3Al and TiAl. Han, C.S., Kim, J.W., Kim, Y.W.: Journal of Korean Institute of Metals and Materials, 2009, 47[3], 147-54