(106819)Microstructures and mechanical properties of oxide dispersion strengthened CoCrFeNi high-entropy alloy produced by mechanical alloying and spark plasma sintering

摘要

1.2 Hf and 1.5 Y_2O_3 (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 Cr_7C_3 and Cr_2O_3, and a few of MnCr_2O_4 is only detected in CCFN HEA. High-density Y_2Hf_2O_7 with the average diameter of 6.9 ± 4.2 nm uniformly distribute in the matrix and Cr_7C_3 of ODS-CCFN. Lattice misfit calculations indicate that Y_2Hf_2O_7 particles exhibit a coherent interface with the matrix, and a semi-coherent interface with Cr_7C_3. The average sizes of all phases, including grain, Cr_7O_3 and Cr_2O_3, 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 Y_2Hf_2O_7 and highly refined grains, Cr_7C_3 and Cr_2O_3. The electrical resistivity of ODS-CCFN is lower than that of CCFN, the reason may be that the existence of Y_2Hf_2O_7 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 Y_2O_3.