Impact of B4C ceramic doping on the mechanical and electrochemical properties of AlCoCrFeNi equimolar HEA

Abstract

This work examines the influence of adding 2 % boron carbide (B4C) to an AlCoCrFeNi high-entropy alloy processed by spark plasma sintering under identical conditions. The study combines microstructural characterization, electrochemical evaluation and statistical microhardness analysis to determine how the ceramic addition modifies the behavior of the alloy. Scanning electron microscopy and optical metallography revealed that the undoped alloy presents a relatively uniform matrix with limited contrast variations. In contrast, the B4C-reinforced sample shows a more heterogeneous structure, marked by a broader range of gray levels and a clearer separation of phases. Chromium-rich regions were identified in both materials, consistent with the high melting point of Cr and the solid-state nature of the mechanical alloying route. In the doped sample, boron and carbon tended to accumulate within these Cr-rich domains, following their mixing enthalpy preferences. Electrochemical testing in chloride solution indicated that the addition of B4C reduces corrosion resistance, with the doped material exhibiting lower stability during open-circuit measurements and a decreased charge-transfer resistance in impedance spectra. Mechanical testing showed that the 2 % B4C addition increases Vickers hardness, although the hardness distribution becomes less uniform, as reflected by a higher dispersion in the statistical parameters. Overall, the results indicate that B4C reinforcement strengthens the alloy but introduces greater microstructural heterogeneity and compromises corrosion performance.