Influence of gravity on the microstructure of directionally solidified Al-In monotectic alloy

To investigate the influence of gravity on the microstructure of directionally solidified Al-In monotectic alloy, downward U.D.S. (direction to gravity) and upward U.D.S. (opposite direction to gravity) was carried out. To realize downward U.D.S., zone-melting method was introduced in order to eliminate cavity which inevitably appears in front of solid/liquid interface in current Bridgman method. A hyper-monotectic alloy, Al-18.0 mass%In, was used to examine gravitational segregation on both primary and monotectic L₂(In) phases. (1) The gravitational macro-segregation and their condensation of primary L₂ liquid were observed 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 morphology. On the monotectic reaction, macro-segregation of L₂ liquid growing cooperatively with α(Al) phase was not observed neither in upward 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 layer with the length of several hundred μm was found in front of solid/liquid interface. The length of In-rich layer in downward U.D.S. was twice longer than in upward U.D.S. in each 6 level growth rate, 1-32 mm/h. (3) Influence of growth rate to the interphase spacing between fibrous monotectic In phases reveal no remarkable difference between upward and downward U.D.S.