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Full Record for Micrograph 10

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Micrograph no
10
Brief description
Cu 70, Ni 30 (wt%), cored dendrites
Keywords
alloy Link to MATTER Glossary entry for alloy, copper, coring Link to MATTER Glossary entry for coring, dendrite Link to MATTER Glossary entry for dendrite, metal, nickel, partition coefficient Link to MATTER Glossary entry for partition coefficient
Categories
Metal or alloy
System
Cu-Ni   Link to phase diagram
Composition
Cu 70, Ni 30 (wt%)
Standard codes
Reaction
Processing
Chill cast
Applications
Sample preparation
Etched in NH4OH/H2O2
Technique
Reflected light microscopy
Length bar
400 μm
Further information
This alloy is typical of many copper based alloy systems. The dendrite structure shows coring (variation in solute concentration). The light areas are rich in nickel and the darker areas are low in nickel. Chill casting extracts heat quickly enough to prevent significant solid state diffusion, resulting in cored dendrites. The centres of the dendrites that cool near the liquidus temperature, are nickel rich compared to the outer layers that solidify at progressively lower temperatures. Because the partition coefficient is positive the outer layers solidify with progressively lower nickel concentrations. The observed pattern results from the intersection of the plane of polish and the randomly orientated regions of equal solute concentration.
Contributor
Prof T W Clyne
Organisation
Department of Materials Science and Metallurgy, University of Cambridge
Date
25/10/01
Licence for re-use
Attribution-Non-Commercial-Share Alike 2.0 UK: England & Wales
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