Influence of Gravity on Microstructural Transitions in Directional Solidification on Refined Al-Ni Alloys at Low Growth Rates

As a follow-on of the experiments performed during EUROMIR95 and LMS96 on the transition from columnar to equiaxed solidification in a more or less refined aluminium alloy, we have proposed new experiments on multigrain directional solidification in microgravity and on ground, in order to analyse the transitions of the growth morphologies of the more or less equiaxed crystals as a function of the solidification conditions, and the influence of convection on these microstructural transitions. We present here the preliminary results of the experiment AGHF6 performed during the Spacelab-STS95 mission (nov. 98).