Processing and characterization of TiB₂-TiNiFeCrCoAl high-entropy alloy composite

A series of TiB₂-TiNiFeCrCoAl high-entropy alloy (HEA) composites with HEA contents of 5, 10, and 20 wt.% were fabricated to a relative density of above 95% without applied external pressure at 1550°C in flowing argon. Research indicates (i) the formation of liquid HEA is promoted with the assistance of an optimized ball mill process, which facilitates the sintering through a liquid phase sintering mechanism, and (ii) HEA can react with the oxide impurities in TiB₂ and can consequently enhance the densification. Continual observations on microstructures and properties indicate that the sintered composites have a submicronmeter grain size of 0.90±0.11, 0.79±0.09, and 0.74±0.07 μm; a high hardness of 23.3±0.9, 21.6±1.0, and 17.5±1.2 GPa; and a high indentation fracture toughness of 8.7±0.4, 11.1±0.6, and 12.8±0.6 MPa·m^1/2, respectively, for samples with 5, 10, and 20 wt.% HEA. The addition of HEA to TiB₂ can significantly enhance the densification, results in fine microstructures, and improve the mechanical performance.