The Calphad method is a tool of choice for exploring the multicomponent phase space. However, the lack of appropriate thermodynamic databases is currently impeding the development of new multi-principal element alloys (MPEA). The construction of thermodynamic databases for MPEAs presents a particular challenge. In contrast to databases for "conventional" alloys where one element is dominating and a relatively small number of modelled ternary systems is sufficient, a database for MPEAs should include all ternary systems since all elements are, in principle, equally important. At present, this is not quite possible, since many ternary systems, even with common elements, have not been investigated experimentally.
Here we present a relatively small database for the elements Al-Co-Cr-Fe-Mn-Ni-C, which covers the CoCrFeMnNi Cantor alloy with additions of Al and/or C. These alloys are predominantly fcc at high temperature and with the addition of Al increasing amounts of bcc and/or B2 phases are formed. The database contains descriptions of all ternary systems within the Co-Cr-Fe-Mn-Ni system, but some ternary descriptions with Al are still missing. Even within the Co-Cr-Fe-Mn-Ni system a few ternary systems are just thermodynamic extrapolations from their binary subsystems. E.g. Co-Cr-Mn is predicted to be quite complex with large fcc, bcc, hcp, beta-Mn and sigma phase fields, but the system has not been experimentally investigated. This database is now being used to explore the composition space with the goal to find possible precipitation hardening fcc-based alloys with exceptional mechanical properties.