The fabrication of multi-material ceramic components by additive manufacturing enables the combination of different functionalities within a single component, with co-sintering of phases exhibiting different densification kinetics representing one of the key challenges. The aim of this master's thesis was to evaluate the feasibility of fabricating multi-material components based on aluminium oxide (Al2O3) comprising electrically insulating and electrically conductive regions, using thermoplastic material jetting (TMJ) and pressureless rapid sintering (pSPS). Instead of cellulose nanofibers, established in previous research as a precursor for the in situ formation of a graphene-like phase, the applicability of more accessible and easier-to-prepare microcrystalline cellulose (MCC) was investigated.
Thermoplastic suspensions of Al2O3 and of Al2O3 with MCC addition, both with a solids loading of 50 vol.%, were prepared, rheologically characterised and optimised for printing. The suspensions were processed by TMJ into single-material and two-material test specimens, followed by wick debinding and rapid sintering at 1650 °C.
Both suspensions exhibited shear-thinning behaviour and rheological properties suitable for TMJ printing, from which single- and two-material specimens were successfully printed without macroscopic defects. Sintered Al2O3 specimens reached a relative density of 99 % of the theoretical value, while Al2O3 + MCC specimens reached 86.9 %, with the latter exhibiting lower shrinkage. Raman spectroscopy confirmed partial conversion of MCC into a graphene-like carbon structure, resulting in an increase in electrical conductivity of approximately eleven orders of magnitude relative to pure Al2O3. Despite the difference in shrinkage, no cracking was observed at the interface between the phases in the two-material specimens. The results confirm the feasibility of the proposed concept, while also highlighting the need for further optimisation of the suspension composition and homogeneity of the carbon phase.
|
