Effects of cerium on the microstructures and grain sizes of cast TiAl alloys.

The rare earth element cerium (Ce) was added to cast binary Ti-44 at.% Al alloys by arc melting in the range of 0.05 to 0.3 atomic percent. It was observed that the as-cast structures of the ingots consisted of the usual three zones of fine equiaxed grains near the mould wall, columnar grains growing away from the mould wall and coarse equiaxed grains near the center. Ce greatly promoted the growth of columnar grains and reduced their diameters. The ingots were subsequently heat treated to obtain well-defined fully lamellar structures. The material containing no rare earth displayed large equiaxed lamellar colonies of average size of >1400 μm; the material with 0.05 at.% addition of Ce consisted of lamellar colonies of as fine as ∼440 μm. The finest grain size of this material was 320 μm at the top position in the ingot. [ABSTRACT FROM AUTHOR]