Characterization of the CrMnFeCoNi high-entropy alloy system using diffusion multiples

The design of new high entropy alloys (HEAs) has been proven to be extremely challenging due to the high complexity of these metallic systems based on four or more elements. However, some of these systems have exhibited promising properties, which have pushed for their further development. One of these systems is the CrMnFeCoCi alloy, named the Cantor alloy. The production of a diffusion multiple to study the diffusion in this system has provided some interesting results, which were further investigated in this master thesis. Most of this work consisted in the investigation of the phase stability occurring in the Cr45Mn16Fe23Co8Ni8 alloy. This composition was selected based on EDX measures performed on an interesting zone in the diffusion multiple, exhibiting two different FCC phases next to a third unknown phase, to see if such a result could be reproduced. The new alloy was studied in the as cast state, and after several annealings at 1000°C to characterize its microstructure. The analysis of the nano-indentation results performed on both the diffusion multiple and the annealed samples helped to partially link the microstructure present in these different materials. In the meantime, the use of the CALPHAD approach, through the Thermocalc software, has provided predictions, that were useful in some cases, but this approach systematically underestimated the presence of the complex tetragonal intermetallic σ-phase, forming the majority of the sample microstructure. The other phases were a BCC Cr rich phase, and another phase, satisfying the definition of an HEA, whose crystallography is probably FCC, but this could not be confirmed. The results obtained give clarification on the microstructure that could be expected from this alloy, but some observations and further questions remain unanswered, and some new work on the topic may be useful, especially for the characterization of the occurrence and the diffusion processes inside the sigma phase, or about the evolution of the diffusion multiple at other temperatures, and with different annealing durations.