Precipitation-hardened high entropy alloys with excellent tensile properties

To achieve balance of high strength and high ductility remains a difficult problem for metallic materials, especially in as-cast alloys. We combined the design concepts of high-entropy alloys (HEAs) and Ni-based superalloys, and designed two new Ni48.7Co17.5Cr10Fe9.3Al7.5Ti7 and Ni47.7Co17.5Cr10Fe9.3Al7.5Ti7Mo1 (at%) precipitation-hardened cast HEAs. Both two alloys have face-centered cubic (fcc) high-entropy matrix + nano γ′ (Ni3(Al,Ti)-type) particles structure. Fine γ′ particles with the average diameter less than 70 nm and 130 nm are homogeneously distributed in dendritic regions and inter-dendritic regions, respectively. The yield strength of Ni47.7Co17.5Cr10Fe9.3Al7.5Ti7Mo1 alloy is 899 MPa, ultimate tensile strength is 1064 MPa and elongation is 14.3%. The strengthening theory is discussed. Attributable to substantial γ′ precipitates, shearing strengthening mechanism plays an important role. Fracture is caused by micron-sized eutectic γ′ phases that lead to stress concentration.