Microstructure and enhanced mechanical behavior of the Al7Co24Cr21Fe24Ni24 high-entropy alloy system by tuning the Cr content

The single-phase face-centered-cubic Al7Co24Cr21Fe24Ni24 (in atomic percent, at%) high entropy alloy lacks sufficient hardness and strength at room temperature, which restricts its structural application in the future. To strengthen this material, the (Al7Co24Cr21Fe24Ni24)(100-x)Cr-x (x = 0, 11, 20, and 26) high entropy alloys were prepared and investigated. We found that with increasing the Cr content, the volume fraction of the BCC phase enriched with Al, Fe, and Cr elements increased gradually. In the BCC-contained HEAs, ordered B2 particles were always dispersed in the BCC solid solution, which resulted in a dramatic enhancement of comprehensive mechanical properties. Nanoindentation measurements showed that both the nanohardness and the elastic modulus values of the BCC phase are much greater than that of the FCC phase. The room-temperature compression test showed that the yield strength significantly increased from 249 MPa to 1649 MPa with the slight sacrifice of the ductility, along with increasing the Cr content. More importantly, the (Al7Co24Cr21Fe24Ni24)(74)Cr-26 alloy exhibits outstanding compression behavior, with the high yield strength (1649 MPa) and fracture strength (2830 MPa) as well as good compressive plastic strain of 24.9%. Furthermore, to facilitate the optimization of the comprehensive properties of alloys, the close correlation between the microstructures and mechanical properties was also discussed.