Effect of carbon fiber reinforcement and sintering temperature on mechanical properties, thermal shock resistance, and oxidation behavior of zirconium diboride formed via material extrusion additive manufacturing

Abstract Two aqueous zirconium diboride (ZrB 2 ) inks, one monolithic and one reinforced with 11 volume % milled carbon fiber, were developed for the additive manufacturing technique of material extrusion. Both inks exhibited nearly identical shear-thinning, yield-stress rheological profiles, allowing for consistent printing parameters. Three pressureless sintering temperatures (1850 °C, 1950 °C, and 2150 °C) were investigated to understand their effect on density, mechanical properties, and thermo-oxidative performance (thermal shock and oxidation resistance). Increasing sintering temperature generally increased the density of both monolithic and carbon fiber-reinforced components, though the latter consistently had lower densities. Mechanical testing revealed that at lower sintering temperatures (1850 °C and 1950 °C), monolithic samples had higher flexural strengths due to greater density, while carbon fiber reinforcement improved Weibull modulus, indicating enhanced reliability. At 2150 °C, both material types showed high Weibull moduli and similar flexural strengths, likely due to microstructural changes, including carbon fiber degradation. Crucially, carbon fiber reinforcement significantly improved thermal shock resistance during oxyacetylene torch testing to simulate a representative extreme environment. The 1850 °C carbon fiber-reinforced print survived the test while the monolithic counterpart cracked instantly. Additionally, the carbon fiber-reinforced samples maintained oxide scale adherence, unlike the monolithic ZrB 2 which experienced severe oxide scale cracking and spallation. This improved oxidative performance is attributed to fiber-like pores formed by carbon fiber oxidation within the oxide scale, accommodating volume contraction of zirconia (ZrO 2 ). This study presents a rapid and low-cost method for developing near-net shapes of carbon fiber-reinforced ZrB 2 with survivability in extreme environments while providing critical insights into the role of carbon fiber incorporation and sintering temperature in the resulting ceramic properties.