Effects of lanthanum on structures and grain sizes of Ti-44Al alloy

By vacuum are melting, lanthanum (La) was added in the range from 0.05 % to 0.3 % (mole fraction) to binary Ti-44 % Al alloy to refine its fully lamellar (FL) colonies for high ductility. Effects of La on structures and grain sizes of the alloy were determined. It was observed that La greatly promoted growth of columnar grains in as-cast structures of the ingots and reduced their diameters. The ingots were subsequently heat treated to obtain well-defined fully lamellar structures. The material without La displayed large average size of equiaxed lamellar colonies over 1400 mu m (resulted from five measurement positions in a sample), and the material with 0.1% addition of La consisted of the finest average lamellar colonies as 381 mu m, the finest grain size was 337 mu m at top position. When La addition was over 0.1%. La stabilized the columnar structure and it was difficult to refine the columnar grains in heat treatment, therefore, grains were coarser.