Lattice imperfections in intermetallic Ti–Al alloys: an X-ray diffraction study of the microstructure by the Rietveld method

Microstructure in intermetallic Ti–Al alloys with compositions (Al=45, 50 and 55%: all compositions are in at. %) in the homogenized bulk and cold-worked powder states has been extensively studied using Rietveld whole X-ray profile fitting technique, adopting the recently developed software, MAUD (Material Analysis Using Diffraction). The analysis also considers the quantitative estimation of different phases and lattice defect related features of the evoluted microstructures, namely crystallite sizes, microstrains, stacking fault probabilities and dislocation density values, etc. in both the states of the materials (homogenized bulk and cold-worked powder). The study revealed reverse α2→γ phase transformations due to plastic deformation in all the considered alloy compositions. Upon cold-working, high densities of stacking faults were observed in the α2-Ti3Al microstructure, accompanied by moderate values (∼1011 cm−2) of average dislocation densities in the γ-TiAl microstructure. In the homogenized bulk alloys, the respective Vickers microhardness values were found to be 464, 365 and 339 HV, decreasing with increase in Al concentration. The values of all the above defect parameters have been evaluated and compared for elucidating a better structure-property relationship.