240_l19_supp - Copper Aluminum Alloys This Al-Cu phase...

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Copper Aluminum Alloys This Al-Cu phase diagram shown only goes up to ca 60%, by weight, of Copper. and is “split” at around 54wt%Cu by a particular phase. This "split" means that the two parts of the diagram must be considered separately. The diagram up to the 54% point is very similar to the "standard" phase diagram. Intermetallic phases are not named " or $ , but are assigned other Greek letters (though there is no strict convention for this). Here the phase on the right is named 2 , but other than its name it is dealt with in exactly the same way as a beta phase.
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Cu-Al Phase Diagram " " + liquid liquid 2 + liquid " + 2 Cu 2 Al, 2 The eutectic composition is at 33%Cu/67%Al, and the T e is ca. 550 K. A 25%Cu/75%Al composition is known as a hypoeutectic alloy A 36%Cu/64%Al composition is correspondingly called hypereutectic
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Micrographs: Eutectic Alloy Micrographs are high-resolution microscope pictures which may be produced by techniques such as reflect light microscopy (RLM, top), scanning electron microscopy (SEM, bottom) or scanning transmission microscopy (STM). As a liquid is cooled at the eutectic composition, the two phases grow simultaneously as an interconnected structure which forms the solid eutectic phase. The phase has a lamellar structure, which consists of many thin alternating layers of the two components. The lamellar structure ensures that there are very small diffusion fields head of the solid-liquid interface, meaning that atoms do not travel over very significant distances for the two phases to simultaneously form. The RLM picture shows the co-operative formation of
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240_l19_supp - Copper Aluminum Alloys This Al-Cu phase...

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