SOME UNIQUE ASPECTS OF TRANSMISSION ELECTRON-MICROSCOPY AND SPECTROMETRY FOR PRESENT AND FUTURE STUDY OF INTERMETALLIC COMPOUNDS

Although dislocation cores are difficult to analyze in TiAl alloy, an attempt has been made to correlate them with the macroscopic properties of single-phase gamma alloys with additions of Cr, Mn or Nb. The surface energies of planar faults such as intrinsic stacking faults and antiphase boundaries are derived from the core structure of dislocations and compared with available ab initio calculations. Analytical transmission electron microscopy was also used to investigate other parameters that influence TiAl plasticity, with special attention devoted to the role of oxygen. Finally, spectrometry techniques such as extended absorption fine structure (EXAFS) and extended electron energy loss fine structure (EXEELFS) are introduced to study the atomic local environment. From these experiments, a phonon ''soft-mode'' is suspected in TiAl. An attempt is made to evaluate the feasibility of EXEELFS experiments at very high spatial resolution for investigation of the core of dislocations.