Mechanisms Of Phase-Transformation In Low-Temperature Irradiated Nial

Phase transformations induced by low‐temperature (15 K), heavy‐ (Xe) and light‐ (D) ion irradiation of a monocrystalline NiAl intermetallic compound are investigated via in situ Rutherford backscattering and channeling experiments. Total amorphization of the irradiated layer is observed, whatever the irradiation ion mass, as soon as a mean number of displacements per atom of 0.3–0.4 is reached. On the contrary, the mechanisms of phase transformation appear to be strongly dependent on the cascade regime. Light‐ion irradiation leads to a sigmoidal shape of the amorphization kinetics, suggesting that amorphization takes place by a defect accumulation process. Heavy‐ion irradiation shows a more complex behavior with the formation of a premartensitic phase prior to amorphization. An interpretation of this new type of phase transformation is presented in terms of defect cascade disordering and damage‐induced stresses.