Crystalline to amorphous transformation in NiAl: ion irradiation studies in relation to cascade parameters

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Abstract
The transformation from the crystalline to the amorphous state of NiAl (B2 structure) in mixed multilayered thin films has been studied by in situ electrical resistivity measurements during ion irradiation at 77 K. Microstructural states are characterised by transmission electron microscopy observations. Kinetic behaviour shows that amorphisation is induced by an intracascade process and occurs only for heavy-ion irradiations. The influence of the cascade parameters on damage formation is investigated by varying the energy and mass of the irradiating projectile. The role of energy density, therefore, appears crucial in the collapse to the amorphous state. A reordering mechanism via enhanced radiation defect mobility is suggested. Results for irradiations with low-energy recoils with very dilute cascade structure are explained. Mechanisms are discussed in relation to previous amorphisation studies on irradiated metallic or semiconductor systems. The role of antisite defects is also emphasised for the transition towards topological disorder.