The effect of microstructure on the hardness and oxidation behavior of SPSed ZrB2-SiC and TiB2-SiC for thermal protection systems

ZrB 2 is a leading candidate for TPS in reentry vehicles owing to its high melting point, thermal shock resistance, and low density. It improves oxidation resistance when composited with SiC. Since TPS is used in the airframes of reusable space vehicles, it must possess excellent mechanical properties. To achieve this, the manufacturing process was optimized. ZrB 2 -SiC and TiB 2 -SiC with different composition ratios were fabricated through SPS. The microstructure was most densified sintered at 1900 °C and for 10 min. A comparison of the microstructures of TiB 2 -SiC and ZrB 2 -SiC mixtures revealed that the TiB 2 particles had agglomerated and grown into coarse grains, indicating that the sintering conditions significantly affect microstructure formation. The ZrB 2 -30 vol%SiC and TiB 2 -15 vol%SiC mixtures had the highest Vickers hardness, at 2345(HV5) and 3223(HV5), respectively. These samples were selected for subsequent oxidation testing. For TiB 2 -15SiC, the depth of the oxidation reaction layer increased with oxidation time at 1250 °C. For ZrB 2 -30SiC, the oxide layer thickened with increasing oxidation time, and passive oxidation only occurred at 1250 °C. At 1650 °C, a non-oxidized ZrB 2 layer was observed beneath the oxide layer, whereas the TiB 2 -15SiC sample shattered. ZrB 2 -SiC was proved to a promising material for TPS owing to its superior mechanical properties and excellent oxidation resistance. • ZrB 2 -SiC and TiB 2 -SiC composite with SiC between 15 and 30 vol% were fabricated SPS and successfully densified was achieved under sintering conditions of 1900 °C for 10 min. • The composite with the highest hardness was a mixture of ZrB 2 -30SiC and TiB 2 -15SiC, reaching 2345 and 3223 Hv, respectively. TiB 2 -15SiC showed significantly higher hardness. • In ZrB 2 -30SiC, the oxide layer thickened with increasing oxidation time and passive oxidation only occurred at 1250 °C. • At 1650 °C, SiC depleted layer formed beneath the oxide layer. • The oxidation reaction layer of TiB 2 -15SiC increased with oxidation time at 1250 °C, whereas it shattered at 1650 °C.