Variant Orientation Distribution in a Near-γ Ti-Al Alloy with a Lamellar Microstructure

An original approach based on semi-automatic treatment of Kikuchi patterns collected by Transmission Electron Microscopy is used to analyse the a2 an g variant distributions in a quaternary TiAl-based alloy (Ti-48at.%Al-2%Cr-2%Nb), with two lamellar microstructures of different fineness. Statistic data analysis shows that neither g variant orientations nor interface misorientations are randomly distributed within a given grain. The largest deviation from randomness is observed for the coarser microstructure. We also pointed out the presence of g|g subboundaries between same but slightly misoriented variants, as well as the existence of some semicoherent g|g twins accommodated by dislocation lattices. The analysis of the misorientation distributions of g|g and g|a2|g interfaces suggests that a variant selection occurs during growth and coarsening stages of the a ® a2 + g transformation process.