High-resolution electron microscopy study of defect structures in -TiAl irradiated with 15 keV He ions in a high-voltage transmission electron microscope

Abstract

γ-TiAl intermetallic alloy specimens were irradiated with 15 keV He ions to a dose of 8.6×1020 ions m−2 (4.6 dpa, averaged in the range of the irradiation damage distribution in depth from 0 to 240 nm) in a high-voltage transmission electron microscope (HVTEM) at room temperature. The defect clusters formed during the ion irradiation were characterized with high-resolution transmission electron microscopy (HRTEM). Induced defect clusters are mainly planar defects and rotated domains (RDs). The planar defects have the edges parallel to {111) of the matrix and several nanometers in size. They are formed during ion irradiation and remain stable even after annealing and correspond to the bright streaks along <111] in selected area diffraction (SAD) patterns of the ion-irradiated specimens. The RDs, which are rotated 90° to the matrix, are formed in as-irradiated and post-irradiation annealed specimens. They are identified by the appearance of super-lattice reflection spots in SAD pattern and by image contrast in HRTEM observation as well. Post-irradiation annealing at 673 K for 30 min enhanced the formation of the RD. The mechanism of formation of the RD is discussed.