Sc doping induced the mechanical property improvement of dual-phase high-entropy alloy

To tailor the generation and proportion of precipitated phase in high entropy alloys (HEAs) to achieve mechanical property improvement, Sc, known as a rare-earth element, is introduced into an equimolar AlCoCrFeNi HEA with a dual-phase structure. Hence, (AlCoCrFeNi)100-xScx HEAs (x = 0, 0.5, 1 and 2, at.%) are fabricated, and also the phases, microstructures, compressive behaviors and strengthening mechanisms are studied in detail. When introducing the Sc element, HEA microstructure evolves from a single BCC structure to a hypoeutectic structure. The hypoeutectic structure contains the primary BCC phase and eutectic region, in which the eutectic region is comprised of BCC phase and Laves phase. With an increase of Sc addition, the yield strength exhibits an improvement from ∼1293 to ∼1441 MPa due to solid solution strengthening and precipitated phase strengthening. However, the fracture strain decreases from 32.5% to 23.6%, and meanwhile compressive strength lowers from ∼2352 to ∼2018 MPa due to high stress/strain concentration stemming from the incompatibility of elastic and plastic deformation between precipitated eutectic phase and primary BCC phase. Moreover, the brittle fracture mechanism of the present alloy system is identified.