Mechanisms of phase transformation in low-temperature irradiated NiAl

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Abstract
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.