The crystallization and growth of AlB₂ single crystal flakes in aluminum

An in situ high temperature heat treatment was used to investigate the crystallization and growth behavior of AlB₂ flakes in aluminum. Aluminum samples containing 1.8% boron were heated above the liquidus and then rapidly cooled through the Al_(L) + AlB₁₂ region to avoid the formation of AlB₁₂ crystals. Subsequently, a homogeneous distribution of high aspect ratio AlB₂ flakes crystallized upon holding below the peritectic transition temperature. Growth rate in the (a) and (c) dimensions increased during elevated hold temperatures below the peritectic transition temperature. Surprisingly, faster cooling rates from above the liquidus to room temperature resulted in thinner, wider flakes. Similar to graphite this phenomenon is believed to result from a need to accommodate a changing misfit strain energy between the solidifying aluminum and the growing AlB₂ flakes.