LAUSR

Abstract Intermetallic titanium aluminides are often alloyed with niobium to improve oxidation resistance and mechanical properties. Depending on the overall alloy composition and on the solubility of the present phases for niobium, new phases may be introduced in the alloys' microstructure upon niobium addition. Here we describe the microstructure of the alloy Ti-42Al-8.5Nb produced by powder metallurgy after annealing at 550 °C and 650 °C. We identify the orthorhombic O-phase within α 2 laths of lamellar (α 2  + γ) colonies by single crystal electron diffraction and high-resolution imaging. Domains of O-phase variants and α 2 phase form columnar crystallites in α 2 (0001) planes having low indexed α 2 {11-20} and {1-100} interface planes. The nm-sized domains are rotated with respect to each other resulting in elastic strains across the domain boundaries. No elemental segregation of Nb was detected in α 2 /O-phase lamellae.