Analysis of the rheology and the relation between the microstructural and mechanical properties of 3D printed 3Y-ZrO2 for dental applications

Abstract

3D printing has been in the in last few years highlighted as the manufacturing technique of the future thanks to the advantages that it provides, enabling the fast fabrication of customized parts without the requirement of special tools such as molds, being potentially a technology that will substitute traditional methods of materials processing. It has already done remarkable steps with plastics, thanks to their low melting temperatures and the easiness of which they can be transformed if compared with other materials families, but nowadays there is a special interest in incorporate it as a feasible technique to be employed in ceramics. This is especially notable in the field of bioceramics, where the possibility of manufacturing customized parts directly from a CAD file could promote remarkable advances in medicine for prosthesis and scaffolds among other applications. In this Master’s thesis the suitability of different compositions of 3Y-TZP ceramics for being 3D printed were investigated. For this, a rheological analysis of three different binders (Pluronic® F-127 hydrogels at different weight proportions with water), obtaining their sol-gel transition temperature. This analysis was then correlated with 3D printing trials performed using different compositions (the three hydrogels charged with ceramic contents ranging from 44 wt. % to 75 wt. %), determining that the most suitable pastes for 3D printing had a 25 wt. % Pluronic® F-127 and a ceramic fraction between 54 wt. % and 70 wt. %. During the 3D printing process and samples preparation several issues had to be dealt with, principally due to large defects in form of non-homogeneities caused during the printing of the samples, and severe fissures appeared during the drying process, with the subsequent complications found during polishing stages, making it difficult to obtain proper samples to be characterised. The microstructural analysis revealed that samples with low fraction of ceramics had insufficient densification while sintering, promoting the presence of high porosity as well as low density. The mechanical characterization through the analysis of hardness, indentation fracture toughness and elastic modulus revealed the good condition of the specimens in terms of mechanical properties and at the same time, their dependence on the porosities and the defects introduced while preparing them to be characterised. Finally, the effect of the existing relative humidity in the environment where the sample were dried on the presence of large defects in the samples was investigated, finding that by letting the samples to dry at an environment of 84% of relative humidity, the presence of cracks generated during the process was mitigated.