Papers by Author: S. Watanabe

Abstract: An atomistic study of radiation-induced amorphization in the NiTi intermetallic compound was performed by using in-situ high-resolution high-voltage electron microscopy and molecular dynamics in conjunction with image simulations. Both theoretical and experimental results show that metastable nanometer-size inherent atomic clusters form and disappear during irradiation, so that a spatiotemporal fluctuation under amorphization is induced. The random formation and annihilation of such inherent nanoclusters are believed to be responsible for these fluctuations, which appear to be related to transitions between the ideal glass state and metastable, unrelaxed states in an energy-dissipative system under irradiation.

Abstract: The formation process of intermetallic compound under Ni+ion implantation into pure Al was studied at lower temperature below room temperature. Ion implantation was carried out using 250KeV ion accelerator. Cascade damage was introduced Ni+ions implantation at 223K without new phase nucleation. However, when Ni+ions were implanted at room temperature, the grown larger plate-like phases were observed during implantation up to 1x1017 Ni+/cm2. Ni concentration in Al matrix and newly formed phase were 0.3-0.5 and 8.5-13.3at%,respectively. It was identified that the formed phases were close to the ordered orthorhombic structure of Al3Ni type. It was also confirmed from observation with high resolution HVEM that these phases grew with continuous ion implantation. Thus it was clarified that cascades act as preferential nucleation site for intermetallic compound, and the phases nucleated at cascades coalesce in the growth process of each phase during continuous implantation through ion irradiation enhanced diffusion.