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 alpha(2) an gamma 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 gamma 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 gamma vertical bar gamma sub-boundaries between same but slightly misoriented variants, as well as the existence of some semi-coherent gamma vertical bar gamma twins accommodated by dislocation lattices. The analysis of the misorientation distributions of gamma vertical bar gamma and gamma vertical bar alpha(2)vertical bar gamma interfaces suggests that a variant selection occurs during growth and coarsening stages of the alpha -> alpha(2) + gamma transformation process.