| The primary objective of this research was to develop a scientific understanding of solidification processes in immiscible (hypermonotectic) alloys and to determine how the directionally solidified structures were influenced by gravity level, translation rate and composition (dome height).; In this research, the Cu-Pb-Al ternary system was used. The Cu-Pb binary is a low dome height monotectic while the Al-Pb binary is a high dome height monotectic. As Al is added to the Cu-Pb binary, the dome height of the binary is thought to increase in a relatively smooth manner. For alloys of monotectic composition, it has been shown that by increasing the Al content in the Cu-Pb monotectic, a transition from an irregular to a regular structure is produced. By using the Cu-Pb-Al system, a range of dome heights can be obtained by varying the composition of the alloy without the further complication of using additional monotectic systems.; Since microstructural variations are anticipated with gravity level, experimentation was carried out aboard NASA's KC-135 zero-g aircraft during parabolic maneuvers. This produced gravity levels ranging from 0.01 to 1.8 g's.; Several alloys were directionally solidified with compositions ranging from 0.9 wt. % Al (low dome height) to 4.2 wt. % Al (high dome height). Translation rates of 5.0, 3.0, 2.0, 1.0, and 0.6 mm/min were utilized. Control samples were also processed at the same rates under one-g conditions.; Results indicate structural variations with g-level, composition (dome height) and translation rate. In low Al content alloys, the average particle size varied with gravity level, whereas in high Al content alloys, the volume fraction varied with gravity level. These variations with g-level resulted in "banded-type" structures where the average particle size or the volume fraction of the hypermonotectic phase was larger during the high-g portion of the maneuver. |
