Solvus
Index
The solvus line represents the locus of solubility limits for the solid solutions in a multicomponent system. For the copper-silver binary system shown two such lines exist, one for the a-phase and one for the b-phase. When a material of fixed composition is cooled through these lines, the single solid phase breaks up into two phases of the same chemical potential.
From: Callister, 
"Materials Science and Engineering," 
Wiley (1994)