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Objective: The aim of this study was to evaluate the mechanical properties of 3D printed zirconia (ZrO2). Materials and Methods: The test specimens were produced with a 3D printer that uses lithography-based ceramic manufacturing (LCM) technique with two different parameters in horizontal and vertical printing orientations. Altogether four groups of nine specimens were printed and examined. Mechanical characterization was performed using 3-point bending test (ISO 10477) and surface microhardness (Vickers) test. Grain structure, porosity and printing layer morphology were examined with optical and scanning electron microscopy (SEM). Additionally fractography analysis was done to investigate and evaluate features of fracture initiation site. Numeric results were statistically analyzed with ANOVA (a = 0.05). Results: The average flexural strength reached for printed zirconia was 499 MPa (+/−75 MPa) for specimens printed in horizontal orientation and 575 MPa (+/−69 MPa) for specimens printed in vertical orientation. Optical microscopy and SEM analysis revealed that fractures initiated between the printing layers or from a local porosity. Printing layer thickness varied from under 13 μm to over 20 μm. Conclusions: The study revealed that 3D printed zirconia has challenges in regards to layer integration. Based on this study, 3D printed zirconia still suffers from low mechanical strength, which together with long carbon-debinding time, does not make 3D printed zirconia a potential material for dental appliances at this stage. Further research is needed to create more suitable zirconia precursor slurries and to optimize printing parameters and sintering conditions to be able to 3D print zirconia with higher mechanical properties. publishedVersion

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Additive manufacturing has been found to be suitable processing method for ceramic materials in recent years. For other material groups, like plastics and metals, the 3D-printing is widely studied and the industrial markets are growing. For ceramics, there is still a lot to study before its potential in ceramic manufacturing can be acquired. Stereolithography (SLA) is one method to 3D-print ceramics. Stereolithography uses photons to initiate polymerization reaction at monomer, oligomer or prepolymer solution. In stereolithography, the ceramic powder is dispersed in monomer medium and polymer network is printed around the particles. These monomer solutions can be the same as used in the plastic stereolithography 3D-printing. Usually the main components of the monomer solution are acrylates, methacrylates or epoxies. To polymerize the monomers, proper photoinitiators is added. Photoinitiator should be chosen according the photon wavelength that the SLA printer is using and the reaction type that it should initiate, radical initiators for acrylates and methacrylates and cationic initiators for epoxies. During this Master thesis work new slurry is tailored and commercial Lithoz GmbH manufactures slurries are studied. Only small components can be made so far. One limiting factor is the layered structure that are prone to the delamination. Delamination leaves cracks and flaws at the surface, reducing the mechanical properties of the ceramic component and bigger components than few cubic centimeters could not be printed with sufficient mechanical properties. The overall processing time of the ceramic 3D-printing is long, even small component takes over a week to process. This is because of the heat treatments that are necessary for the process takes long time. The post thermal curing and polymer degradation at 3D-printed ceramic parts is studied in this Master thesis work. With the newly tailored slurry, consisting from the acrylate-monomer body and aluminium oxide particles, the heat treatment’s total time was reduced significantly compared to the commercial Lithoz GmbH’s slurries. Ceramic components are successfully made and printing properties are studied widely with all slurries. This study also highlights the aspects in stereolithography ceramic 3D-printing that requires further studies.

The thesis is divided into three sections: Background of the study, experimental, and finally discussion. The first part includes the literature survey which discusses the studies related to pulsed laser ablation that have been reported so far in the state-of-the-art. From the second part, the reader can study the fundamentals of the experimental methods used in order to understand the results. The third part of the thesis consists of the results from this study and a discussion on them followed by the conclusions for this thesis project. In this study, green synthesis of TiO2 nanoparticles and carbon nanotubes was successfully demonstrated through pulsed laser ablation in deionised water. The nanoparticle yield for ablated titanium suspensions was found to increase with laser fluence till 40% laser power and then decrease at 50% laser power due to reduced laser fluence but again increase at 60% laser power due to overlapping of laser spots. The yield of nanoparticles in ablated graphite suspensions was independent of laser fluence but proportional to laser power until the power was so high that evaporation of liquid interfered and decreased the yield. The transmission electron microscopy of suspensions from ablated titanium target revealed round crystalline TiO2 nanoparticles surrounded by amorphous phase nanoparticles. X-ray diffraction and wide angle x-ray scattering of these nanoparticles confirmed presence of anatase, rutile and brookite. For ablated titanium target, x-ray diffraction detected titanium monoxide, titanium dioxide and titanium (III) oxide besides titanium metal. The particle size measurements from TEM and SAXS indicated decrease in the average size of TiO2 nanoparticle with the increase in laser power. The transmission electron microscopy of the suspensions from ablated graphite target indicated the presence of carbon nanotubes. X-ray diffraction of the ablated graphite target detected the presence of diamond on the target surface.