Abstract
The development of solidification microstructure in aluminum-rich AlBe alloy powders was studied as a function of melt undercooling, cooling rate, powder size and beryllium content. Auger electron spectroscopy indicates that BeO partially displaces Al2O3 from the powder surface. The BeOAl2O3 coating reduces the attainable undercooling at beryllium contents above about 4 at.% Be. Powders containing Al-9at.%Be when cooled at 0.5 °C s−1 contain facetted primary beryllium and a cellular aluminum matrix. Increasing the cooling rate to 25 °C s− reduces the extent of facetting of the primary beryllium phase, and at a cooling rate of 500 °C s−1 multiple primary beryllium dendrites are observed. In Al-4at.%Be powders cooled at 500 °C s−1, primary beryllium formation is avoided and solidification commences with a cellular aluminum and intercellular beryllium structure. The aluminum cells evolve to a dendritic network during recalescence. Following recalescence the dendritic aluminum and interdendritic beryllium structure is replaced by a coupled eutectic morphology which completes solidification. The microstructure development is analyzed in terms of the solidification pathways possible based on a skewed coupled eutectic growth zone and composite stable-metastable phase diagrams including a metastable liquid miscibility gap.
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