日本金属学会誌

J. Japan Inst. Metals, Vol. 54, No. 12 (1990),
pp. 1320-1328

Crystallization Kinetics of Amorphous Cu50Ti50 Alloy Prepared by Mechanical Grinding

Kuniyasu Nakamura1, Kiyoshi Kasai2 and Michihiko Nagumo3

1Graduate Student, Waseda University, Tokyo
2Graduate Student, Waseda University, Tokyo. Present address: NHK, Tokyo
3Laboratory of Materials Science and Technology, Waseda University, Tokyo

Abstract:

Crystallization kinetics of amorphous Cu50Ti50 alloy prepared by mechanical grinding of the intermetallic compound powder with a high energy ball mill was studied. Kinetics at the isothermal annealing was well analyzed in terms of the Johnson-Mehl-Avrami equation, giving a velocity exponent of 0.85 and an activation energy of 183 kJ/mol. Both figures are less than the corresponding values of the material prepared by a rapid cooling process. Kinetics at the athermal annealing was analyzed using the Kissinger method and an activation energy of 154 kJ/mol was obtained in accord with the analysis with the JMA equation.
The amorphous state and the crystallization process were discussed from these results. In an amorphous material prepared by mechanical grinding, the crystalline fraction remains and is likely to act as nuclei of crystallization. Crystallization is likely to proceed two-dimensionally on these nuclei. The number and average size of nuclei were estimated to be 1024/m3 and of 103 unit cells of Cu50Ti50, respectively.
The activation energy of diffusion estimated by assuming the two-dimensional crystal growth kinetics is 214 kJ/mol and the diffusion of Ti atoms is likely to be rate-controlling. Atom migration necessary for the crystallization is considered to take place in a short range of the order of 5-10 nm.


(Received 1990/8/17)

Keywords:

amorphous alloy, mechanical grinding, solid state reaction, ctystallization kinetics, diffusion


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