Papers by Author: Takeshi Nagase

Abstract: Pinpoint nano-crystallization in Fe-based metallic glass was achieved by 2.0MV electron irradiation. Circular nano-crystalline structure regions with about 1μm in diameter were formed in the metallic glass and they were well dispersed in the amorphous matrix. In Fe77.5Nd4B18.5 alloy, micrometer order hard magnetic nano-composite region was formed in non-magnetic metallic glass matrix by electron irradiation. Electron irradiation induced crystallization is very effective for obtaining superior functional metallic materials with fine magnetic domains.

Abstract: Formation of a nanocrystalline structure through rapid solidification, thermal crystallization and electron irradiation induced crystallization was investigated in Fe-Nd-B alloys. A nanocrystalline structure was obtained by rapid quenching of the melt in a Fe86Nd9B5 alloy, while an amorphous single phase was formed in a Fe77Nd4.5B18.5 alloy. In the latter alloy, a nanocrystalline structure was obtained by thermal crystallization and electron irradiation induced crystallization of the amorphous phase. The average grain size of the precipitate obtained by irradiation at 298 K was about 8 nm, which is much smaller than that obtained during thermal crystallization. Results indicate that electron irradiation is effective for obtaining a novel nanocrystalline structure in Fe-Nd-B alloys.

Abstract: Superplastic viscous deformation and thermal crystallization behavior of supercooled liquid in Zr60.0Al15.0Ni25.0 metallic glass were investigated. The temperature interval of the supercooled liquid region (∆Tx) was 83 K. The supercooled liquid showed significant viscous plasticity, resulting in large elongation and high strain rate deformation. The stress-strain behavior can be classified into three types: stress overshoot, stable viscous flow with constant flow stress and strain hardening. The strain hardening is due to the precipitation of Zr6Al2Ni crystalline phase with ellipsoidal morphology. Superplastic viscous deformation behavior is very sensitive to thermal crystallization as well as to deformation temperature and strain rate.