High-resolution electron microscopy of gamma-TiAl irradiated with 15 keV heliu ions at room temperature

gamma-TiAl intermetallic alloy was irradiated with 15 keV He+ to a dose of 8.6 x 10(20) ions m(-2) (4.4 dpa) in a high-voltage transmission electron m icroscope (HVTEM) at room temperature, and the evolution of irradiation def ects was observed during and after irradiation with HVTEM and high-resoluti on transmission electron microscopy (HRTEM). induced defect clusters in gam ma-TiAl became visible with HVTEM to an irradiation dose of 4.7 x 10(19) io ns m(-2) (2.4 x 10(-1) dpa). They are mainly planar defects and have a char acter of domain structures with the edges parallel to {1 1 1} of the matrix and several nanometers in size. Cavities (He bubbles) with irregular shape s were observed in gamma-TiAl after He+ irradiation of 5.7 x 10(20) ions m( -2) (2.9 dpa). Post-irradiation annealing at 673 K for 1800 s enhanced the growth of the domain structure. The analysis of HRTEM images and selected a rea diffraction (SAD) patterns suggests the formation of rotated domain (RD ) which has the same structure as the matrix but in orientations rotating 9 0 degrees to the matrix. The mechanism of formation of the RD in gamma-TiAl crystals is discussed. (C) 1999 Elsevier Science B.V. All rights reserved.