INTERPARTICLE SPACINGS AND UNDERCOOLINGS IN Al-Si EUTECTIC MICROSTRUCTURES.

Modified methods for the measurement of interparticle spacing and undercooling of the Al-Si eutectic have been applied in an attempt to test the applicability to this system of the accepted equation for diffusion-controlled normal eutectic growth. Good agreement with some published measurements has been obtained. For the unmodified and chill-modified eutectic microstructures it seems probable that the basic equation is applicable but that the extremum condition is not. For the impurity modified eutectic there is no agreement with the theoretical prediction, although the possibility is advanced of adding an undercooling term based on twin boundary energy.