Columnar to equiaxed transition during growth of a univariant eutectic

In this work the transition from columnar to equiaxed growth is studied during the solidification of the univariant eutectic L -> alpha(Al) + theta-Al2Cu in the ternary Al-Cu-Ag system. The experimental technique used is upwards solidification with a controlled cooling rate. In the lower part of the sample where the temperature gradient is high, a cellular eutectic is observed. When the temperature gradient decreases, the morphology first changes into two-phase dendrites and finally into an equiaxed eutectic. When the amount of Ag is increased, the formation of eutectic colonies becomes easier. Also, a higher cooling rate facilitates the formation of eutectic colonies. The addition of TiB2 does not influence the nucleation of eutectic colonies. Although the composition is on the eutectic groove, primary alpha(Al)-dendrites are found in the samples with TiB2. This leads to segregation effects due to the density difference between alpha(Al) and the liquid.status: publishe