Strengthening and toughening mechanism of low-density (Ti, Zr, Nb, Cr, M)B₂-SiC high-entropy ceramics (M=Mo, Ta)

This paper reports a low-density (Ti, Zr, Nb, Cr, M)B₂ (M=Mo, Ta) high-entropy diboride (HEB) ceramic system and reveals the coupling relationship between bond strength, densification behavior, and mechanical properties through Mo/Ta comparison. HEB-SiC composite ceramics were fabricated via the two-step strategy involving B₄C thermal reduction and vacuum hot pressing. The (Ti, Zr, Nb, Ta, Cr)B₂-30 vol% SiC composite achieved a relative density of 99.1%, accompanied by outstanding comprehensive mechanical properties: microhardness (31.9 ± 1.08 GPa), Young's modulus (503 ± 15 GPa), flexural strength (425 ± 10 MPa), and fracture toughness (5.71 ± 0.29 MPa·m^1/2). Microstructural observations confirmed the presence of high-density stacking faults in α-SiC grains, as well as the crystallographic orientation relationship (101)_α-SiC//(100)_HEB. A synergistic toughening mechanism based on “stacking fault–bridging–deflection” was proposed. Furthermore, a good correlation between first-principles predictions and experimentally measured mechanical properties was established, realizing a closed-loop validation among computation, experiment, and mechanistic interpretation.