Grain growth and strengthening mechanisms of ultrafine-grained CoCrFeNiMn high entropy alloy matrix nanocomposites fabricated by powder metallurgy

Ultrafine-grained CoCrFeNiMn high entropy alloy matrix nanocomposites reinforced by nanoparticles were fabricated by thermomechanical consolidation of high energy mechanically milled powders. TiO(C) nanoparticles in the CoCrFeNiMnTi0.15 sample make the FCC matrix grains clearly finer than those in the CoCrFeNiMnNb0.1 sample with NbC and (Cr, Mn)(3)O-4 nanoparticles (average grain size: 503 +/- 184 vs 778 +/- 274 nm). Quantitative analysis reveals that drag force for grain growth during consolidation in the CoCrFeNiMnTi0.15 sample is higher than that in the CoCrFeNiMnNb0.1 sample due to the higher Zener force from the TiO(C) nanoparticles. The microstructural difference renders the yield strength of the CoCrFeNiMnTi0.15 sample to be almost 50% higher than that of CoCrFeNiMnNb0.1 sample (1243 vs. 831 MPa). To elucidate this phenomenon, the strengthening mechanisms are systematically analyzed and a model considering grain boundary dislocation emission is established to account for the interaction between grain boundary strengthening and nanoparticle strengthening. This model explains the different effects of NbC, (Cr, Mn)(3)O-4 and TiO(C) nanoparticles, and estimates the yield strength better than the existing models. (C) 2019 Elsevier B.V. All rights reserved.