IN-SITU TEM STUDY OF ION-INDUCED AMORPHIZATION AT LOW-TEMPERATURE IN AL3TI

Phase modifications induced at low temperature (T less-than-or-equal-t o 40 K) in Al3Ti by ion irradiation were investigated by in situ trans mission electron microscopy (TEM). Irradiation with heavy ions induces a complete amorphization at a dose of approximately 1 dpa. After part ial chemical disordering, a crystalline phase change from the DO22 str ucture into the L1(2) structure is observed only after the onset of am orphization. These results suggest that a lattice strain release is pr oduced by the amorphization process allowing the transition towards a higher symmetry phase. On the other hand, light ion irradiation leads to partial chemical disordering and to strong lattice distortions, but the transition c-a is not completely achieved at doses higher than 2 dpa.