Enhanced mechanical properties of high pressure solidified CoCrFeNiMo0.3 high entropy alloy via nano-precipitated phase

CoCrFeNiMo0.3 high entropy alloy was prepared by vacuum arc melting. The effects of different solidification pressures on the microstructure and mechanical properties of CoCrFeNiMo0.3 high entropy alloy were investigated. All ambient pressure (0.1 MPa) Mo0.3, 4 GPa Mo0.3 and 7 GPa Mo0.3 alloys exhibit two kinds of structures. The FCC structure is the solid solution matrix, and the precipitated phase enrich in Cr and Mo (sigma phase) is distributed in the grain boundary of the matrix phase. With the increase of the test pressure, the size of the precipitated phase gradually decreases and the volume fraction increases obviously, and tends to form nano-scale particles. Meanwhile, the precipitated phase gradually diffused into the matrix due to the increase of the pressure. The results of nanoindentation tests show that the hardness of the alloy increases significantly with the increase of solidification pressure, especially that of 7 GPa Mo0.3 alloy, which is about 2 times that of 0.1 MPa Mo0.3 alloy. The strengthening mechanism of CoCrFeNiMo0.3 high entropy alloy with increased pressure is mainly nano-precipitated strengthening. This present findings not only pave the way for designing the structure and property regulation of high pressure solidified HEAs but also promote the application orientation of various property combinations. It provides the theoretical basis for its application and is expected to be used as structural materials in various fields.