Characteristic orientation relationships in nanoscale Al-Al2Cu Eutectic

A fully lamellar Al-Al2Cu eutectic comprising alternate nano-scale α-Al and θ-Al2Cu phases was synthesized through laser surface remelting of a cast Al-32.7 wt% Cu alloy. The orientation relationship between α-Al and θ-Al2Cu phases was investigated from Kikuchi patterns obtained using electron backscattered diffraction (EBSD) and t-EBSD techniques. The characteristic orientation relationship (OR), {211}Al2Cu||{111}Al and 〈120〉Al2Cu||〈110〉Al, was observed independent of interlamellar spacing. This OR has two variants where, besides the two parallel planes, the variant I exhibits (001)Al2Cu||{001}Al and the variant II exhibits (001)Al2Cu||{111}Al. Variant I prevails over variant II in laser-processed α-Al and θ-Al2Cu nano-laminates, and atomistic modeling indicates that this is due to the low energy interfaces associated with variant I, i.e., {211}Al2Cu||{111}Al or (001)Al2Cu||{001}Al. A comprehensive understanding of the crystallographic orientation relationships between two phases may help predict or explain the active slip systems in fine-scale Al-Al2Cu eutectic and other cubic-tetragonal two-phase materials.