Coaxial direct ink writing of multiple continuous carbon fiber bundles-reinforced Al2O3–SiC–C castables with enhanced mechanical properties

Abstract

To enhance the strength and fracture toughness of Al₂O₃–SiC–C (ASC) castables, additive manufacturing based on a coaxial nozzle direct ink writing (DIW) process was employed to fabricate ASC castables reinforced with multiple groups of continuous carbon fiber bundles. The influence of bentonite addition (0–2 wt.%) as a rheological modifier on the viscosity, thixotropy, and viscoelastic behavior of the slurry was systematically investigated. A flow field model was established to analyze the effects of printing parameters and the number of introduced fiber bundles on the extrusion behavior of the slurry. Results revealed that increasing the thickener content improved the structural stability and shear-thinning behavior of the castable, while its thixotropy first increased and then decreased. The optimal structural recovery and flowability were achieved at a bentonite content of 1.5 wt%. During extrusion, continuous carbon fiber bundles (0, 1, 2, and 3 bundles) were introduced, corresponding to optimal air pressures of 0.25, 0.25, 0.40, and 0.40 MPa, respectively. The castable effectively encapsulated the fibers, forming printed structures with high dimensional accuracy. After sintering at 1500 °C, SiC whiskers were generated on the fiber surfaces due to reactions between SiO/Si and carbon sources. Consequently, the flexural strength of the ASC castable increased from 4.3 MPa (without fibers) to 7.6 MPa (with three fiber bundles), while the fracture toughness rose from 573 J to 1093 J. Therefore, the introduction of continuous fiber bundles markedly improves the mechanical reliability of the DIW-fabricated ASC castables.