Phase diagram

Graphic illustration of the various states and phases of alloys as a function of temperature and composition.

Depending on the number of components of the respective alloy, binary (two substances), ternary (three substances) or quaternary (four substances) systems are distinguished that can be displayed in phase diagrams.

Phase diagrams are derived from a thermal analysis or dilatometric measurements. From the holds derived from the thermal analysis displaying liquidus and solidus temperatures, the temperature values of the phase change between liquid and solid can be applied in a diagram according to the respective alloy composition to get the applicable phase diagram (Fig. 1).

Figures 2 and 3 illustrate examples of phase diagrams of binary and ternary systems. The most important phase diagram for iron casting is the iron-carbon phase diagram.

(Source: Hasse, Stephan: Foundry Lexicon (19th, revised edition), specialist publisher Schiele & Schön, Berlin, 2008)


  • Fig. 1: Derivation of the phase diagram from the cooling curve of a two substance system A - B with complete solubility in the liquid and solid phase
  • Fig. 2:  Binary iron - copper phase diagram
  • Fig. 3: Ternary chromium - iron - nickel phase diagram