Interfacial engineering reaction strategy of in-situ Cr23C6/CoCrFeNi composites with network structure for high yield strength

Abstract

CoCrFeNi high-entropy alloy (HEA) has distinctive properties such as high hardness and good corrosion resistance, however, its low strength or poor yield strength at room temperature limits its wide-range applications in industry. Herein, Cr₂₃C₆ particles reinforced CoCrFeNi composites with graphene nanoplates as a precursor were fabricated using in-situ reaction spark plasma sintering and cold rolling annealing processes. Results showed that the microstructure of the CoCrFeNi HEA and their composites were face-centered cubic structures before and after annealing, and Cr₂₃C₆ particles were precipitated inside the matrix during SPS. The precipitated Cr₂₃C₆ particles exerted strong pinning forces to migrate dislocations and grain boundaries, effectively refining the grains during the annealing process. After cold rolling, Cr₂₃C₆/CoCrFeNi composites showed a typically banded deformation structure. After annealing, fine equiaxed grains were distributed around the deformed grains, and the proportion of equiaxed grains was increased with the annealing time. The yield strength (YS) of Cr₂₃C₆/CoCrFeNi composites was significantly higher than that of CoCrFeNi alloy after cold rolling and annealing. When annealed for 20 min, the YS and elongation of Cr₂₃C₆/CoCrFeNi composites with 0.3 wt% graphene addition were 1100 MPa and 6 %, respectively. The YS was 68.2 % higher than that of the CoCrFeNi alloy. We have identified that the improvement of mechanical properties of Cr₂₃C₆/CoCrFeNi composites is mainly attributed to grain refinement, dislocation strengthening, precipitation strengthening, and load transfer strengthening, among which dislocation strengthening plays a major role.