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Nucleation Phenomenon during Solidification of Metal Matrix Composites.

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Final rept. 30 Sep 90-30 Mar 94,

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A detailed analysis of possible interfaces in cast aluminum silicon base reinforced particle composites containing SiC, Al2O3 and C indicates that several different kinds of interfaces can form. The reinforcements may be totally surrounded by primary-phase, or primary silicon, or by the eutectic between Al and Si. In addition, in some cases, some of the original coatings or their reaction products in the case of coated particles like nickel or nickel-aluminum intermetallics in nickel coated reinforcements, Cu or Cu-aluminum intermetallics in Cu coated reinforcements may also form the interface. The reaction between dispersoids and the alloy itself can form a complex interface. These different interfaces have also been experimentally observed in the microstructures of cast particulate composites, with the exception of primary a-aluminum surrounding the reinforcement. The absence of alpha-aluminum on the reinforcements is attributed to possible lack of nucleation, persistent lateral growth and a thermal lag between the reinforcement and the matrix. Estimates of works of adhesion for the different interfaces observed in cast composites have been made using the London Van der Waal equation, correlated to the properties of the composites, and used to identify the possibilities of further improving these properties.

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  • Laminates and Composite Materials

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