Structure–property correlation in a novel ZrB2–SiC ultrahigh-temperature ceramic composite with Al-alloy sinter additive

In this study, the effect of minor (5 vol.%) addition of Al–10Si–0.2Mg (composition in wt.%) pre-alloyed powder on densification, microstructure and mechanical behaviour of spark plasma-sintered ZrB2-20 vol.% SiC composite has been investigated. The sintered composite records a relative density of 99.83% despite being processed at a relatively low temperature (1700 °C) in argon atmosphere. Interestingly, ZrB2–20SiC–5AlSiMg composite does not undergo any shape distortion though the liquidus temperature of this metallic alloy additive is quite low (~ 592 °C). Extensive phase and microstructure analyses by appropriate techniques indicate that no free or unreacted AlSiMg is detected in the sintered composite. Thermodynamic analysis suggests that AlSiMg serves as a reducing agent for ZrO2 oxide scale and forms respective high-melting oxide phases. Raman analysis confirms that incorporation of 5 vol.% AlSiMg enhances residual compressive stress of SiC grains. Furthermore, the addition of AlSiMg is found to enhance the thermal shock resistance of the composite. In brief, this new AlSiMg additive results in better densification (99.83%) and hence an attractive combination of useful mechanical properties like Vickers microhardness (17.63 ± 0.54 GPa), nano-hardness (18.62 ± 1.23 GPa), indentation fracture toughness (7.21 ± 1.13 MPa $$\sqrt {\text{m}}$$ ), elastic modulus (432.64 ± 32.90 GPa) and flexural strength (659.25 ± 32.40 MPa) in the AlSiMg-added ZrB2-20SiC composite.