Additive manufacturing of fibre-reinforced ceramics

Abstract

Bioceramics, such as hydroxyapatite (HA), are commonly employed as artificial implants due to their ability to significantly enhance bone ingrowth and stimulate the activity of natural bone cells. The implantation of an artificial bone structure becomes necessary when a bone defect exceeds a critical size. While HA has outstanding bone ingrowth capacities, its drawback lies in its limited mechanical properties, making it unsuitable for areas experiencing high mechanical stress.The aim in this thesis is to enhance the mechanical properties of HA bioceramics, using short alumina-silica fibres as reinforcing material for 3D-printable ceramic slurries. The slurries are processed using a Digital Light Processing (DLP) based vat polymerisation, where a photocurable ceramic slurry containing ceramic particles and organic binder is selectively cured by blue light to build up the part layer by layer. Subsequent thermal post-processing produces bioceramic parts characterised by high density with high resolution.Including fibres into the printing process requires changes in processing. Slurries with different short fibre contents were prepared and the following properties were analysed prior to printing: viscosity, agglomerate size and curing depth. Then the printing parameters were adapted to the slurry characteristics. The analysis of the thermal behaviour of the printed parts was carried out to ensure a successful debinding process. The distribution of the fibres in the printed ceramics were analysed by light and scanning electron microscopy. Shrinkage and geometric accuracy of the printed fibre-reinforced components were also investigated, as well as the mechanical properties in terms of three point bending strength. The present thesis proved that 3D printing of fibre-reinforced ceramic slurries was possible using DLP based methods. The fibres inhibited the shrinkage of the ceramics, which let to deformations in small parts, and fibre sedimentation within the first layers. The ceramics showed higher porosities caused by the fibre sizing and poor fibre-matrix adhesion which led to decreasing bending strengths.