Coextrusion of Reaction-Bonded Carbides by Robocasting

Coextrusion by robocasting is a suitable process for fabricating multimaterial ceramic structures. Herein, the robocasting process is used to fabricate core-shell structures, combined with subsequent liquid silicon infiltration (LSI). Thus, reaction-bonded silicon carbide (RBSC), reaction-bonded boron carbide (RBBC), and reaction-bonded silicon-boron carbide composites are produced. The LSI process offers the possibility to circumvent high temperatures and pressures used in traditional fabrication. Pastes with high solid loading and necessary carbon content are used in order to combine the robocasting with the subsequent LSI process. The influence of the paste rheology on the sample fabrication of multimaterial core-shell structures of reaction-bonded carbides is investigated. The key rheological data, such as the viscosities of the combined pastes, are correlated with the observations from the microstructural investigation using scanning electron microscopy. A correlation between the difference in viscosity and the core geometry can be established. Crack formation in the material combination of RBSC and RBBC is found and compared with layered multimaterial structures of reaction-bonded carbides. Residual stresses, which can be used to explain the crack formation, are investigated using Raman spectroscopy.