Microstructural modifications induced by swift ions in the NiTi intermetallic compound

Abstract

The conditions for track formation by irradiation with swift ions, in the shape memory NiTi metallic compound are studied. We observe that tracks are only induced in the monoclinic structure but not in the cubic one and only when the linear rate of energy deposition by electronic excitation ([d E/d x] e) exceeds 46 keV/nm. We show that the tracks are amorphous in their centre and that a decrease of the monoclinic towards cubic transformation temperature is observed at the periphery of the track region. For [d E/d x] e=32 keV/nm, no individual tracks can be observed at low fluences, only a monoclinic → cubic structure transformation is observed at high fluences. If [d E/d x] ⩽ 17 keV/nm, swift ions are unable to induce any visible structural modification by electronic excitations. The track formation in this alloy is discussed within the framework of the classical Coulomb explosion and thermal spike models.