Effect of Fe content on microstructures and mechanical properties of eutectic Co-Cr-Fe-Ni-Hf multi-principal element alloys

In order to reduce the cost, the present study develops a series of Co-Cr-Fe-Ni-Hf eutectic multi-principal element alloys (MPEAs), exhibiting an increased Fe content from 10 to 75 at%. When increasing Fe content, the eutectic microstructure changes from regular eutectics to cellular eutectics, both of which consist of alternative FCC and Laves phases. The microstructural morphology relates to the fusion of entropy, namely a smaller value favors the cellular eutectics and vice versa. The mechanical performance is mainly determined by the eutectic morphology. Regular eutectics leads to low strength and large plasticity; cellular eutectics exhibits high strength and low plasticity. The mechanical performance of cellular eutectics containing a part of regular eutectics depends on the fraction of regular eutectics. When the cellular eutectics contains a small fraction of regular eutectics, the crack is easy to nucleate and propagate along the regular eutectics, which is harmful to the plasticity. The high-ferrous eutectic MPEAs predominantly exhibit eutectic morphology and show large strength with a decent plasticity.