Growth of facetted microvoids in Zn–Fe–Sc quasicrystal

Abstract

Microvoids, the size of which ranges from 1 to 50 µm in diameter, have been observed on the fracture surface of a millimeter-sized single icosahedral quasicrystal of stable Tsai-type Zn–Fe–Sc. The shape of the voids consists of planes related to the icosahedral symmetry, typically a dodecahedron with additional truncations by the planes perpendicular to the 2- and 3-fold axes. During controlled cooling from the melting point, approximately 824°C, and additional annealing at 650 ∼ 700°C, the growth of the microvoids was observed. Corresponding to the increase of the size, the number density of voids is decreased so as to conserve the total volume of the voids, i.e. the porosity. This is the first direct evidence indicating that the growth process is essentially Ostwald ripening. The origin of the growth between 600 and 800°C is considered to be not the supersaturated thermal vacancies, but vacancies coming from nearby shrinking voids. The growth is well explained by a thermally activated process with activation energy approximately 3.1 eV.

Keywords:

• void
• quasicrystal
• icosahedral phase
• Tsai-type

Acknowledgements

We thank Ryou Maezawa and Ryuhei Takahashi for their collaboration, and Conradin Beeli for interesting comments. This work has been supported by a Grant-in-Aid for Exploratory Research.