Abstract
The metastable high/medium-entropy alloys (H/MEAs) composing L12 nano-precipitates exhibit outstanding mechanical properties. In this work, the effect of carbon (C)-microalloying on the precipitation behavior and mechanical properties of (FeCoNi)90Al10 MEA was systematically investigated. With the addition of 0.2 at. % C, the yield strength of the alloy increased from 290.4 ± 1.3 MPa to 343.1 ± 2.8 MPa, the ultimate tensile strength increased from 648.5 ± 3.5 MPa to 686.1 ± 3.2 MPa, and the uniform elongation slightly increased after ageing for 45 min. C-microalloying resulted in a decrease of 0.85 kJ/mol and 0.26 kJ/mol in Gibbs free energy for face-centered cubic matrix to L12 and B2 phase transitions, facilitating the segregation of Al atom. This promoted the precipitation of L12 and B2 phases during ageing treatment, which enhanced ordering strengthening. The discontinuous precipitation was promoted at grain boundary after C-microalloying, providing an impetus for the movement of grain boundary. Meanwhile, the movement of grain boundary and the pinning of grain boundary by body-centered cubic precipitates resulted in the formation of grain boundary serration, which could release intergranular strain localization during deformation. Moreover, C-microalloying promoted the formation of planar slip and Taylor lattice during the deformation process, thus improving the plasticity. This finding provides a significant reference for C-microalloying and precipitate control of metastable MEAs.
Published Version
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