Orientation relationships between the icosahedral phase and the α-Al matrix in rapidly solidified Al-Cu-Li-Mg

The morphology of small particles of the icosahedral phase and their orientation relationship with the surrounding α-Al matrix in melt-spun Al-3Cu-1.5Li-1Mg alloys have been investigated, as-spun and after heat treatment, by detailed transmission electron microscopy. The icosahedral phase particles in as-spun Al-3Cu-1.5Li-1Mg are nearly spherical in shape. After heat treatment in the temperature range of 300 to 400°C, the icosahedral phase particles change their morphology into a variety of rod and faceted shapes. The resulting faceted growth shapes are quite different from the triacontrahedron shape reported previously for conventionally solidified particles of the Al₆CuLi₃ phase. The icosahedral phase particles in Al-3Cu-1.5Li-1Mg as-spun and after heat treatment exhibit four different orientation relationships with the surrounding α-Al matrix indicating that the icosahedral phase particles nucleate heterogeneously on growing primary α-Al cells and dendrites during rapid solidification.