Precipitation of a two-dimensional aperiodic approximant phase in Al-rich Al-Mn-Be alloy

Abstract

The precipitation behaviour of a hexagonal two-dimensional aperiodic phase in Al-rich Al-Mn-Be alloy has been investigated. Upon heat treatment at temperatures above 450degreesC, the icosahedral phase formed in a conventionally cast Al-2.5 at.% Mn-3 at.% Be alloy transforms into the stable hexagonal H1 phase. The solute partitioning during transformation leads to the precipitation of a hexagonal two-dimensional aperiodic approximant phase (H' phase). The precipitates have an orientation relationship with the alpha-Al matrix. The similarity of the diffraction features indicates that the hexagonal two-dimensional aperiodic structure of the H' phase is an intermediate structure between the true sixfold quasiperiodic structure and the hexagonal structure of the crystalline counterpart H1 phase.