Multi‐material additive manufacturing of functionally graded ultra‐high temperature ceramics via active in‐line mixing

Abstract Ultra‐high temperature ceramics (UHTCs) are valued for their exceptional mechanical, thermal properties, and oxidation resistance. Among UHTCs, zirconium diboride (ZrB 2 ) reinforced with silicon carbide (SiC) has emerged as a promising candidate for extreme environment applications due to its exceptional combination of high melting point, thermal conductivity, oxidation resistance, and mechanical strength. While most UHTC research has focused on monolithic structures, functionally graded materials offer a novel pathway to further enhance performance by gradually transitioning composition between constituent materials. In this work, a custom‐built direct ink writing (DIW) additive manufacturing system with active in‐line mixing was implemented to fabricate functionally graded ZrB 2 –SiC ceramics. Rheologically optimized aqueous suspensions of ZrB 2 and SiC were formulated with matched viscosity profiles for co‐extrusion. The system enabled continuous and discrete gradient structures by varying composition in real time during printing. Post‐processing involved binder burnout and hot pressing to achieve densification. The graded samples exhibited high relative density (∼93%) and 25% increase in hardness from the ZrB 2 ‐rich to SiC‐rich regions. The elastic modulus in the gradient samples exceeded 517 GPa, which is 2% higher than monolithic ZrB 2 and 78% higher than monolithic SiC. These findings demonstrate the viability of DIW for fabricating dense, graded UHTCs with tunable mechanical properties.