Phase Diagrams

· The lever rule may be used to determine the quantities of each phase present at a given temperature.
· For the point (l) just above the eutectic at (183 + e ) C: C_a = 19.2 wt% Sn, C_E = 61.9 wt% Sn, and C₄ = 40 wt% Sn, so that:
W_a = (C_E - C₄ )/(C_E - C_a ) = 51% , and W_L = (C₄ - C_a )/(C_E - C_a) = 49%

· For the point (m) just below the eutectic,
(183 - e) C, C_a = 19.2 wt% Sn, C_b = 97.5 wt% Sn, and C₄ = 40 wt% Sn, so that:
W_a = (C_b - C₄ )/(C_b - C_a) = 73%
W_b = (C₄ - C_a)/(C_b - C_a) = 27%
· This computation does not indicate the distribution of the a-phase between the Primary and Eutectic structures.

After: Callister,
"Materials Science and Engineering,"
Wiley (1994)