INFLUENCE OF GRAVITY ON THE MICROSTRUCTUR E OF DIRECTIONALLY SOLIDIFIED AL-IN MONOTECTIC ALLOY

To investigate the influence of gravity on the microstructure of direc tionally solidified Al-In monotectic alloy, downward U.D.S.(direction to gravity) and upward U.D.S.(opposite direction to gravity) was carri ed out. To realize downward U.D.S., zone-melting method was introduced in order to eliminate cavity which inevitably appears in front of sol id/liquid interface in current Bridgman method. A hyper-monotectic all oy, Al-18.0 mass%In, was used to examine gravitational segregation on both primary and monotectic L-2(In) phases. (1) The gravitational macr o-segregation and their condensation of primary L-2 liquid were observ ed at the bottom of molten alloy in the downward U.D.S. In the case of the upward U.D.S., the primaries dispersed in aligned monotectic morp hology. On the monotectic reaction, macro-segregation of L-2 liquid gr owing cooperatively with alpha(Al) phase was not observed neither in u pward nor in downward U.D.S. However, the morphology in downward U.D.S . had a tendency to form so called ''banded structure''. (2) In-rich l ayer with the length of several hundred mu m was found in front of sol id/liquid interface. The length of In-rich layer in downward U.D.S. wa s twice longer than in upward U.D.S. in each 6 level growth rate, 1 si milar to 32 mm/h. (3) Influence of growth rate to the interphase spaci ng between fibrous monotectic In phases reveal no remarkable differenc e between upward and downward U.D.S.