Amorphization Kinetics under Electron Irradiation
A.S. Bakai1, A.A. Borisenko1, K.C. Russell2
1
Kharkiv Institute of Physics and Technology, 1 Akademichna str., 61108 Kharkiv, Ukraine
Department of Materials Science and Engineering and Department of Nuclear Engineering,
Massachusetts Institute of Technology, Cambridge, 77 Mass. Ave., MA 02139, USA
2
Corresponding author: Tel./Fax: +38 057 3350854, e-mail: borisenko@kipt.kharkov.ua
PACS: 61.80.Az; 61.82.Bg
Keywords: amorphization; electron irradiation; interphase boundary.
Electron irradiation affects the kinetics of phase transformations not only because of the diffusion increase due to Frenkel’s pairs production, but also due to activation processes at the interphase boundaries. In
paper [1] a new model for the kinetics of phase transformations under electron irradiation was developed. We
apply it to consider the electron-irradiation-induced amorphization as a particular case.
We assume that nucleation of a new phase occurs due to accumulation of radiation damage in defective
regions, including e.g. point defects complexes, a dislocation core sector, a boundary, a triple joint or other structure defects which substantially increase the local free energy. The growth (dissolution) rate of an amorphous
precipitate contains contributions both from thermodynamic driving force and relaxation of irradiation-induced
nonequilibrium atomic configurations at the crystal-amorphous boundary. These contributions are denoted uth
and u irr respectively:
u  dR dt  uirr  uth ,
(1)
where R is the radius of an amorphous precipitate. We argue that contributions uirr and uth have different signs.
The thermodynamic driving force “pushes” the boundary atoms to the phase with the minimal free energy (the
crystalline one). Irradiation, on the contrary, “pushes” the atoms to the amorphous phase, if the probability of
relaxation of the nonequilibrium boundary atomic states into the amorphous phase is higher than into the crystalline one. Therefore, the next criterion for the irradiation-induced amorphization is obtained:
uirr  uth .
(2)
Using criterion (2), the critical electron flux, needed for amorphization at a certain temperature, and the
irradiation dose required for amorphization are derived.
The formulae derived are applied to fit the experimental results on the electron-irradiation-induced
amorphization of Zr3Fe [2].
[1] A.S. Bakai, A.A. Borisenko, K.C. Russell, Problems of Atomic Science and Technology 4(87) (2005) 108.
[2] A.T. Motta, L.M. Howe, P.R. Okamoto, Journal of Nuclear Materials 270 (1999) 174.