TEMPERATURE-DEPENDENCE FOR ION-INDUCED AMORPHIZATION OF NIAL

Crystalline NiAl films of equiatomic composition were irradiated with 360 keV Xe+ ions in the temperature range 4-300 K. The amorphous volume fraction was monitored continuously as a function of ion dose from in situ electrical resistivity measurements. The experimental results indicate that the ion-induced amorphization occurs always by a direct (i.e. intracascade) mechanism. The ion dose necessary for producing complete disorder (i.e. amorphization) increases rapidly between 77 and 120 K. Above these temperatures, the amorphous volume fraction reaches a saturation value lower than 1, indicating that total amorphization is never obtained. The damage cross-sectional area decreases with increasing temperature and this behavior is analyzed by Morehead and Crowder's model. These results suggest that there is under irradiation a competition between ballistic amorphization and heterogeneous irradiation-enhanced crystallization.