Effect of ceramic-binder interface on the mechanical properties of TiB₂-HEA composites

A non-equiatomic CoCrFeNiMo high-entropy alloy (HEA) was used as a binder for the TiB₂-HEA composites. The TiB₂–6 vol% HEA and TiB₂-10 vol% HEA composites were successfully fabricated by mechanical alloying and spark plasma sintering. Phase analysis revealed the presence of FCC and TiB₂ phases in the composites. A detailed microstructural study using scanning electron microscopy and transmission electron microscopy helped with the understanding of the impact of carbide/binder interface on fracture toughness and strength of the TiB₂-HEA composites. TEM revealed a few nanometer-thick intermediate layer between the TiB₂ and HEA phases that facilitates the enhanced wettability between ceramic and binder phase. The fracture mode was affected by the HEA binder concentration, i.e., the dominant mode of fracture changed from intergranular to transgranular as binder content increased from 6 vol% to 10 vol%. The relative density, Vickers hardness and fracture toughness of TiB₂-10 vol% HEA composite reached up to 98.50 ± 0.30%, 22.00 ± 0.62 GPa and 9.23 ± 0.45 MPa m^1/2, respectively. The high fracture toughness of the TiB₂-10 vol% HEA composite was the result of the synergism of high densification, excellent wettability, crack deflection, crack bridging, and transgranular fracture of the TiB₂ particles.