Outstanding yield strength of CoCrNiTa0.1 medium entropy alloy under the synergistic regulated with nanoprecipitation and grain refining

Abstract

CoCrNi medium-entropy alloy (MEA) with equimolar multi-component has attracted much attention due to its promising comprehensive mechanical properties. However, the lack yield strength at room temperature limits its further engineering applications. In order to improve the yield strength at room temperature of CoCrNi MEA, tantalum (Ta) element with larger atomic radios and higher elastic modulus was added into CoCrNi MEA to produce precipitated strengthening phase, and CoCrNiTa0.1 MEA was designed and prepared. The CoCrNiTa0.1 MEA has outstanding yield strength of ~1339 MPa due to the fine grain strengthening and precipitation strengthening, which is much stronger than that of CoCrNi MEA. The as-produced alloy was composed of Ta-enriched Laves phase and fine-grained face-centered cubic (FCC) phase with certain amount of annealing twins. The small grains contributed to a superior fine grain strengthening up to about 434 MPa. The precipitated Ta-enriched Laves phase also greatly enhanced the alloy’s mechanical strength. During the tensile deformation, nanoscale Laves phase particles interacted with the dislocations and annealing twins, hindering the deformation, and thus, significantly improved the yield strength.