Frank–Kasper phases

Applications of TCP phases as high-temperature structural and superconducting materials have been highlighted; however, they have not yet been sufficiently investigated for details of their physical properties.

In 1958, Charles Frank and John S. Kasper, in their original work investigating many complex alloy structures,[1][2] showed that non-icosahedral environments form an open-end network which they called the major skeleton, and is now identified as the declination locus.

The three Laves phases are intermetallic compounds composed of CN12 and CN16 polyhedra with AB2 stoichiometry, commonly seen in binary metal systems like MgZn2.

Due to the small solubility of AB2 structures, Laves phases are almost line compounds, though sometimes they can have a wide homogeneity region.

The sigma (σ) phase is an intermetallic compound known as the one without definite stoichiometric composition and formed at the electron/atom ratio range of 6.2 to 7.

Small extents of σ phase considerably decreases the flexibility and impairment in erosion resistance.

While addition of refractory elements like W, Mo, or Re to FK phases helps to enhance the thermal properties in such alloys as steels or nickel-based superalloys, it increases the risk of unwanted precipitation in intermetallic compounds.