On the comparsion of additive-free HfB2-SiC ceramics sintered by reactive hot-pressing and spark plasma sintering

Ultra-high-temperature HfB2-SiC ceramics were produced by reactive hot-pressing (RHP) and spark plasma sintering (SPS) successfully. In the former case, a mixture of Hf/Si/B4C, mechanically mixed in molar ratio 2.2/0.8/1, was "in-situ" converted into HfB2 and SiC, and then directly hot-pressed until full density was achieved. In the SPS case, a powder mixture of HfB2 + 30vol% SiC was fully densified at 2,100°C, 100°C/min heating rate and 2 min dwell time. The microstructure in both the materials consisted of faceted diboride grains, finer in the RHP case, with SiC particles evenly distributed intergranularly. The combination of some thermo-mechanical properties was of considerable significance. Flexural strength of the RHP fabricated material measured at 25 °C and 1,500 °C in ambient air was 770?35 and 310?15 MPa, respectively. A relevant merit characterized fracture toughness and flexural strength of the material produced by SPS: the values measured at room temperature (3.9?0.3 MPa?m and 590?50 MPa, respectively) did not decrease appreciably at 1500 °C (4.0?0.1 MPa?m and 600?15 MPa, respectively).