Approximant phases, phason planes and domain-boundary networks in Al−Ni−Rh alloys

Abstract

Structurally complicated ξ′- and ξ-phases have been found, for the first time, in as-cast Al₇₃Ni₅Rh₂₂ and Al₇₅Ni₁₅Rh₁₀ alloys. The lattice parameters of these two phases were determined by means of electron diffraction and high-resolution transmission electron microscopy (HREM). These two phases have similar orthorhombic structures but with different lattice parameters of a = 23.2 Å, b = 16.4 Å, c = 12.0 Å for the ξ′-phase and a = 20.3 Å, b = 16.4 Å, c = 14.8 Å for the ξ-phase. A new two-dimensional domain-boundary network has also been observed in these two phases. Domain boundaries with normals closely parallel to the [001] direction are actually phason planes represented by a translation vector of r =(1/2)a +(1/2τ)c in the ξ′-phase and r=±(1/2τ²) a +(τ/2)c in the ξ-phase, whereas the newly-found wide and zigzag boundaries perpendicular to the above set were attributed from the step-like boundary structures of domains related by a translation vector of r =(1/τ)((1/2)a +(1/2τ)c). The structural difference between the two types of planar faults is discussed.

Acknowledgements

We appreciate the editing and English language assistance provided by Drs. Edmund F. and Rhoda E. Perozzi of the Beijing University of Technology. This work is supported by National Science Foundation of China Grant No.GZ032/9 and China State Key Projects of Basic Research Grant No. 2002CB613500.