Copper (Cu)

1
Binary eutectic system (example, silver-copper)
The two constituents are not completely soluble
in each other
Copper (Cu) FCC 0.128 nm atomic radii
Silver (Ag) FCC 0.144 nm atomic radii
Mix 50 Ag 50 Cu, gives two solid phases (a
and b)
a (saturated - mostly Cu with some Ag)
b (saturated - mostly Ag with some Cu)
Not this!
2
Eutectic composition liquid
3
Eutectic reaction
Liquid, L
a L
b L
b
a
Eutectic Reaction (at eutectic temperature
and composition)
a b
Crystal of one phase forms (via diffusion in the
liquid)
Local area becomes depleted of one constituent.
The depleted area near the solidification pushes
the local composition into a solid forming range
on the phase diagram. This causes the
second solid phase to form adjacent to the first
phase.
4
Eutectic reaction
Local area becomes Depleted in the second phase
constituent
Second solid phase forms
5
Eutectic reaction
The 2 phases grow side-by-side creating
a laminated microstructure
6
Eutectic reaction
Eutectic reaction Characteristic microstructure
laminates of each of the 2 phases