Effect of elastic collisions and electronic excitation on lattice structure of NiTi bulk intermetallic compound irradiated with energetic ions

• Published in: Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms Beam interactions with materials and atoms, 2018-07, Vol.427, p.14-19
• Main Authors: Ochi, M., Kojima, H., Hori, F., Kaneno, Y., Semboshi, S., Saitoh, Y., Okamoto, Y., Ishikawa, N., Iwase, A.
• Format: Article
• Language: English
• Subjects: Elastic collisions; Electronic excitation; Energetic ion bombardment; NiTi intermetallic compound; Transformation of lattice structure
• ISSN: 0168-583X; 1872-9584
• DOI: 10.1016/j.nimb.2018.04.035

•For 1–16 MeV ions, the accumulation of elastic collisions causes the A2 structure.•The A2 structure does not exist in the phase diagram.•For the high Se ions, the electronic excitation leads to the A2 structure.•The amorphization of NiTi samples is well correlated to the PKA energy spectrum.•With increasing the PKA energy, amorphization occurs with smaller dpa values. NiTi bulk intermetallic compound with the B19′ structure was irradiated with 1 MeV He, 5 MeV Al, 16 MeV Au and 200 MeV Xe ions, and the change in lattice structure near the surface by the ion bombardment was investigated by using the grazing incidence X-ray diffraction (GIXD) and the extended X-ray absorption fine structure (EXAFS). The lattice structure transformation by the irradiation strongly depends on ion species and/or energies. For the 1 MeV He irradiation, the lattice structure changed from B19′ to the A2 structure, but did not show an amorphization even after the high fluence irradiation. For the 5 MeV Al irradiation, the samples are partially amorphized. For the 16 MeV Au irradiation, the lattice structure of the NiTi samples changed nearly completely from the B19′ structure to the amorphous state via the A2 structure. The value of dpa (displacement per atom) which is needed for the amorphization is, however, much smaller than the case of the Al ion irradiation. For the 200 MeV Xe ion irradiation, the lattice structure completely changed to the A2 structure even by a small ion fluence. The dependence of the lattice structure transformation on elastic collisions (dpa), the spectrum of the primary knock-on (PKA) atoms and the density of energy deposited through electronic excitation was discussed.