Lever Rule

The lever rule is a tool used to determine weight percentages of each phase of a binary equilibrium phase diagram. It is used to determine the percent weight of liquid and solid phases for a given binary composition and temperature that is between the liquidus and solidus.

In an alloy with two phases, α and β, which themselves contain two elements, A and B, the lever rule states that the weight percentage of the α phase is

where

  • a is the weight percentage of element B in the α phase
  • b is the weight percentage of element B in the β phase
  • c is the weight percentage of element B in the entire alloy

all at some fixed temperature.

Read more about Lever Rule:  Derivation

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