Directional solidification of Al- Ni/SiC composites during parabolic trajectories

Aluminum-6.1 wt pct nickel-silicon carbide composites containing varying volume fractions and particle sizes of SiC were directionally solidified at different translation rates and temperature gradi-ents, under variable gravity levels. The gravity level was changed by solidifying the composites in a Bridgman type directional solidification furnace aboard NASA KC-135 aircraft, flying on parabolic trajectories. It was observed that high gravity, high volume fractions of the particles or high effec-tive viscosity of the liquid favors the engulfment of particles by the melt-interface. Solidification in low gravity seems to deflocculate the SiC particle agglomerates while opposite results are obtained when solidifying under high gravity. Intercellular spacings are found to be higher in low gravity so-lidification as compared to high gravity solidification. These results are discussed in terms of the influence of gravity on various physical phenomena involved in the solidification process of the above composite. This paper is based on a presentation made in the symposium “Experimental Methods for Microgravity Materials Science Research” presented at the 1988 TMS-AIME Annual Meeting in Phoenix, Arizona, January 25-29, 1988, under the auspices of the ASM/MSD Thermo-dynamic Data Committee and the Material Processing Committee.