1. 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 (  and  )  (saturated - mostly Cu with some Ag)  (saturated - mostly Ag with some Cu) Not this! Binary eutectic system (example, silver-copper) The two constituents are not completely soluble in each other

2. Eutectic composition liquid Liquid, L  + L  + L    +  Eutectic temperature Eutectic composition Eutectic reaction: One liquid phase becomes two distinct solid phases upon cooling L  +  cooling

3. 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. Eutectic reaction Liquid, L  + L  + L    +  Eutectic Reaction (at eutectic temperature and composition)

4. Second solid phase forms Local area becomes Depleted in the second phase constituent Eutectic reaction Liquid, L  + L  + L    + 

5. The 2 phases grow side-by-side creating a laminated microstructure Eutectic reaction Liquid, L  + L  + L    + 

6. Eutectic reaction: Characteristic microstructure: laminates of each of the 2 phases Eutectic reaction Liquid, L  + L  + L    + 