A new strategy of tailoring strength and ductility of CoCrFeNi based high-entropy alloy

In this paper, a new strategy of high entropy alloy is presented, high strength and promising ductility are realized by precipitation strengthening mechanism. The structure of nano-L1(2) precipitates on the FCC high entropy alloy (HEA) matrix is formed, by adding Ni and Al with a fixed stoichiometric ratio (keeping Ni: Al = 3:1, Ni3Al) to CoCrFeNi matrix. The study found that the mechanical properties of the alloy can be effectively controlled by optimizing the addition of Ni3Al content. Through tension test and theoretical analysis, we found that, when the addition of Ni3Al reaches 0.75, the HEA exhibits the excellent comprehensive strength and ductility. With the tensile fracture strength, yield strength and elongation are 1200 MPa, 910 MPa, and 14%, respectively. Compared with the CoCrFeNi high entropy alloy without precipitates, the yield strength is increased by three times. TEM analysis and theoretical calculation show that the strengthening mechanism of the second phase is the main factor to improve the properties.