Phase Diagrams

· Solving these two equations for W_A and W_B gives the Lever Rule:
W_B = (C_A - C₀ )/(C_A - C_B) and W_A = (C₀ - C_B) /(C_A - C_B)
· For Cu-Ni alloy at 1250 C and a mean composition of Cu-35 wt % Ni the binary phase diagram shows that:
C_S = 43 wt% Ni, C_L = 30 wt% Ni, and C₀ = 35 wt%Ni
· Substituting these values into the lever rule gives the weight percent of the two phases present at 1250 C:
W_S = 38 %, W_L = 62 %
· Changing the temperature of the alloy will change the composition of both the solid and the liquid. These compositions are read from the intersection between the isotherm and the liquidus and solidus lines. The weight fraction of the solid will go between zero and one as the temperature falls from the liquidus to the solidus with the mean composition unchanged.