In this study

a microstructure control strategy by combining powder high-energy ball milling

spark  plasma sintering and hot extrusion was proposed. The influence of preparation process parameters on the evolution of grain size

second phase particles and twins was investigated. A CoCrFeNiMnTi

0.2

high entropy alloy with multi-scale heterogeneous microstructure containing coarse grains

fine grains and nanoparticles

and a CoCrFeNiMnTi

0.2

high entropy alloy consisting of ultrafine grains

nanoparticles and nano-twins were prepared. The tensile mechanical properties showed that the yield strength and elongation

to fracture of the high entropy alloys were up to 1298 MPa and 13%

and 1507 MPa and 7%

respectively

achieving a good trade-off between strength and plasticity. Lastly

based on the revision of the Holpage coefficient

a strengthening model for nanoparticle reinforced ultrafine grain CoCrFeNi-based high entropy alloy was established. A new coupling mechanism between nanoparticles and heterogeneous structure

as well as a synergetic mechanism of ultrafine grains

nanoparticles and nano-twins were discussed. It was also found that nano-twins could increase the flow stress of high entropy alloy

resulting in multi-level deformation behavior by inducing nucleation of new deformation twins.