Papers by Author: Kenji Amiya

Abstract: Nanoscale structural change in (Fe0.5Co0.5)72B20Si4Nb4 bulk glassy alloy on annealing has been investigated using transmission electron microscopy. On annealing at temperatures above 773K, electron diffraction intensity analysis showed a clear structure change for a Cr23C6-type local atomic ordering. The local structure formation of Cr23C6-type nanophase was confirmed by nanobeam electron diffraction. A development process of dense precipitates of the Cr23C6-type nanophase was further studied by high-resolution electron microscopy. It was found that the formation of the highly-dense nanoprecipitates provides an increase in Vickers hardness.

Abstract: Mg-8Zn-4Al-xY base alloys containing an icosahedral quasicrystal phase (i-phase) as a main strengthening phase were prepared by casting into a copper mould at moderate cooling rates. The Y addition was effective for decreasing the size of i-phase and the more homogeneousness of its dispersed state. The mechanical properties at room temperature were much superior to those of AZ91 alloy. The creep tests indicated a promising high temperature creep resistance of the quasicrystal-reinforced Mg-Zn-Al-Y cast alloy. The dislocation characteristic in crept specimens which containing i-phase and no i-phase was analyzed and strengthening mechanism was discussed.