Takayoshi Ozawa1 and Yoichi Ishida2
1Graduate School, University of Tokyo, Tokyo
M\"ossbauer spectrum of tin atoms segregated at the grain boundary of Zn-Al eutectoid was analyzed in regard to the binding state of impurity elements located at the grain boundary. The segregation of impurity atoms is generally considered as the major cause of the grain boundary brittleness. It is interesting to know whether the phenomenon can be explained by the binding state of the segregated impurity atoms.
The present alloy is of two phases, but the grain size is small. The solid solubility of the tin atoms in both phases is very low and no intermetallic compound should occur. Consequently, the ratio of tin atoms segregated at the boundary is large even in an equilibrium state.
Experimental conditions to analyze the electronic and vibrational state and the diffusion constant of the segregated tin were examined at first. A M\"ossbauer source nucleus 119 mSn was doped at 100∼250°C, while the measurement of the spectrum were carried out at -190∼-113°C.
Changes in the spectrum with the doping temperature were explained by the diffusion of tin atoms through the boundary, α and β grains.
It was concluded that the spectrum doped at 100°C was due mainly to tin atoms segregated at the grain boundary. The peak position of the spectrum showed that the average density of S electrons at the tin nucleus site is much higher than that of tin in solid solutions and almost equal to that of isolated tin, while the change in the peak area with the specimen temperature indicated that the Debye temperature and average force constant of the segregated tin are much lower than that of tin in solid solution.
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