Formation of a Nanoscale hcp Structure by Crystallization of an Amorphous Co_<91>Zr_7B_2 Alloy

概要

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A mostly single hcp phase with grain sizes ranging from 3 to 10 nm was found to form as a metastable phase in the crystallization process of an amorphous Co_<91>Zr_7B_2 alloy. The temperature range, in which the nanoscale hcp structure forms, extends from 800 to 900 K and the further heating above 900 K causes the phase transition to ε-Co+Co_<23>(Zr, B)_6. No distinct grain growth in the hcp structure is seen in the temperature range of 800 to 900 K. The hcp phase has a lattice parameter of a=0.2507 nm and c=0.4066 nm which is slightly different from that of pure ε-Co presumably because of the dissolution of Zr and B. The Co_<91>Zr_9 amorphous alloy crystallizes directly to a mixed phase of ε-Co+cubic Co_<23>Zr_6 with a large grain size of about 0.4μm through a polymorphic-type crystallization mode. It is therefore concluded that the addition of a small amount of boron is essential for the formation of the nanoscale hcp structure.
東北大学の論文
1992-03-25