TiNiFeCrCoAl high-entropy alloys as novel metallic binders for TiB^sub 2^-TiC based composites

This paper studies the utilization of TiNiFeCrCoAl high-entropy alloys (HEA) as the metallic binders (10 wt%) in various ceramic matrix (TiB2, 60 wt% TiB2–40 wt% TiC, TiC). Using laboratory synthesized ultra-fine ceramic powders, all samples can be pressureless densified to relative densities over 97% at temperatures of 1550 °C (for TiB2 and TiC) and 1600 °C (for TiB2-TiC). The sintered samples have significantly enhanced properties including fine grain size (~ 0.8–1.5 µm), high hardness (~ 18.6–21.6 GPa), and high fracture toughness (~ 8.7–11.1 MPam1/2). Comparing within these samples, the results indicate the TiB2-HEA sample has the best combination of fine microstructure and good mechanical properties (hardness ~ 21.6 ± 1.0 GPa, fracture toughness ~ 11.1 ± 0.6 MPa m1/2) while the TiC-HEA sample has relative large grain size and acceptable mechanical properties (hardness ~ 18.6 ± 1.1 GPa, fracture toughness ~ 8.7 ± 0.8 MPa m1/2). Hardening and toughening mechanisms are further discussed.