Since already phase diagrams of binary systems can reveal complicated properties of the mixtures of two
components it is quite obvious that a ternary system (mixtures of three constituents) can show much
more complicated features of mixing. We will not focus on any detail in what follows but
only discuss ways of presenting phase diagram data which at least needs three parameters
and the fraction of two components) to specify one point (one thermodynamic state) in a phase
Fig. 2.14 shows as an example of a pseudo-binary phase diagram a selected path from ”pure” to ”pure” , i.e. each ”component” is already a specific composition of two of the three pure components forming the ternary system. Such phase diagrams are highly significant, e.g. for a systematic scan for new ceramics.
In general at least a three dimensional plot is needed to represent phases in a ternary system.
A schematic representation of isothermal sections is shown in Fig. 2.15. Most often a set
of isothermal slices are chosen, e.g. to illustrate the temperature dependence of different
To characterize the composition of a ternary system the famous Gibbs triangle (as shown in Fig. 2.16) is used which has the following features:
The points marked in Fig. 2.16 b) have molar fractions in percent as shown in the following table:
Here we will only discuss one example of Cu doping of a NiTi alloy. NiTi is (one of) the most important shape memory alloys, i.e. it can show switching of the shape driven by temperature changes. This needs for a transition from martensitic to austenitic phase and a martensitic micro-structure containing many twin grain boundaries (B2 phase). For binary Ni-Ti the phase field of B2 phase is very narrow and sensitive to slight fluctuations in composition. The compositional field where the B2 phase exists is broader for Cu doped NiTi and thus allows for the production of elastocaloric thin films.
© J. Carstensen (TD Kin II)