Investigation of microstructure and mechanical properties of HfB2-HfC-TiC-B4C composites

To examine the microstructure and mechanical properties of boride-carbide composites, four quaternary composites with the following chemical compositions were synthesized: 70HfB2-10HfC-10TiC–10B4C (7HHTB), 70HfB2-10HfC-10TiC–10B4C/Nb (7HHTB/Nb), HfB2-HfC-TiC-B4C (HHTB), and HfB2-HfC-TiC-B4C/Nb (HHTB/Nb). These composites were densified using the spark plasma sintering (SPS) method at 2000 °C. The phase composition and microstructure were analyzed through X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM). The sintering performance of all composites was assessed by measuring relative density using the Archimedes method. Hardness and fracture toughness were determined via Vickers indentation and crack length measurements. The findings indicated that solid solutions of (Hf_1-xTi_x) B₂ and (Hf_1-xTi_x) C formed during sintering, with higher quantities present in composites with equal volume fractions of constituents compared to those with a 7:1:1:1 ratio, as well as in samples containing 2 wt% Nb versus those without. The highest fracture toughness recorded value was 5.7 MPa m^0.5, with a maximum hardness of 30.6 GPa, for the fully dense HHTB/Nb composite, which also exhibited the finest grain size of 0.52 μm.