TiNiFeCrCoAl high-entropy alloys as novel metallic binders for TiB2-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 degrees C (for TiB2 and TiC) and 1600 degrees C (for TiB2-TiC). The sintered samples have significantly enhanced properties including fine grain size (similar to 0.8-1.5 mu m), high hardness (similar to 18.6-21.6 GPa), and high fracture toughness (similar to 8.7-11.1 MPam(1/2)). Comparing within these samples, the results indicate the TiB2-HEA sample has the best combination of fine microstructure and good mechanical properties (hardness similar to 21.6 +/- 1.0 GPa, fracture toughness similar to 11.1 +/- 0.6 MPa m(1/2)) while the TiC-HEA sample has relative large grain size and acceptable mechanical properties (hardness similar to 18.6 +/- 1.1 GPa, fracture toughness similar to 8.7 +/- 0.8 MPa m(1/2)). Hardening and toughening mechanisms are further discussed.