Microstructures and mechanical properties of oxide dispersion strengthened CoCrFeNi high-entropy alloy produced by mechanical alloying and spark plasma sintering

Abstract

1.2 Hf and 1.5 Y2O3 (wt.%) were added into CoCrFeNi (CCFN) high-entropy alloy (HEA) to fabricate oxide dispersion strengthened CoCrFeNi (ODS-CCFN) composite by mechanical alloying and spark plasma sintering. Microstructures, including XRD, SEM, EBSD, and TEM of CCFN and ODS-CCFN HEAs were investigated to identify the effects of introducing nano-sized oxides into CCFN HEA. These HEAs compose of FCC matrix and a small amount of Cr7C3 and Cr2O3, and a few of MnCr2O4 is only detected in CCFN HEA. High-density Y2Hf2O7 with the average diameter of 6.9 ± 4.2 nm uniformly distribute in the matrix and Cr7C3 of ODS-CCFN. Lattice misfit calculations indicate that Y2Hf2O7 particles exhibit a coherent interface with the matrix, and a semi-coherent interface with Cr7C3. The average sizes of all phases, including grain, Cr7C3 and Cr2O3, are highly refined in ODS-CCFN. The effects of microstructure changes on properties of CCFN HEA were also detected. Compared with CCFN, the tensile yield strength of ODS-CCFN increases from 978 MPa to 1.25 GPa with a reasonable elongation decreases from 2.6% to 1.9%. The increase in yield strength for ODS-CCFN is mainly ascribed to the precipitation strengthening of Y2Hf2O7 and highly refined grains, Cr7C3 and Cr2O3. The electrical resistivity of ODS-CCFN is lower than that of CCFN, the reason may be that the existence of Y2Hf2O7 particles reduce the lattice distortion of the matrix, and make the electrical resistivity decrease. The corrosion resistance of ODS-CCFN HEA is highly improved in both sulfuric acid solution and sodium chloride solution because its passive current density is largely reduced by the addition of Hf and Y2O3.