Exsolution in phase diagrams
A binary solid solution can show a phase diagram as follows:
The solidus and liquidus separate the single phase regions. This is similar to the Cu-Ni phase diagram. If the system demonstrates exsolution, then there will be a region in the solid state where two solid phases form from the solid solution. This is common and most solid solutions demonstrate it to some degree.
In a eutectic phase diagram, the two-phase solid region meets the solidus/liquidus.
Solid solution regions are usually denoted with Greek letters, for example α for ferritic iron and γ for austenitic iron.