Phase Diagrams
The Lever Rule

· The microstructure and compositions of the phases present are shown on the partial diagram for a Cu-35 wt% Ni alloy ( 65 wt% Cu, 35 wt% Ni)
· The equilibrium mass fraction of each phase present in a two phase zone is estimated using the "Lever Rule."
· For a zone with two phases A, B present, total mass conservation requires:
WA + WB = 1
where WI is the mass fraction of I.
· From conservation of constituents: 
WA CA + WB CB = C0 1

From: Callister, "Materials Science and Engineering," Wiley (1997)