Ordering of the fibrous eutectic microstructure of Al-Al3Ni due to accelerated solidification conditions

Directional solidification experiments with eutectic Al-Al3Ni alloys were p erformed in which the solidification front was accelerated or decelerated c ontinuously. The temperature gradient at the solid/ liquid interface could be kept constant. At a fixed position in all samples processed, the absolut e velocity was, however, the same, independent of the velocity with which t he solidification started. The microstructure perpendicular to the growth d irection was analyzed with respect to average fiber distances, number of ne arest neighbors and the distribution of these quantities. An order paramete r is defined to describe the deviation from a perfect hexagonal arrangement . Inasmuch as the acceleration changes from negative to positive values, th e arrangement of the fibers comes closer to a perfect hexagonal lattice. Th e experimental observations are described and interpreted qualitatively. (C ) 2000 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All rights reserved.