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The effect of second phase addition of zirconia on the mechanical response of textured alumina was analysed. Highly textured monolithic tape-casted alumina was obtained through templated grain growth. Compositions containing 1, 2, 5 and 10 vol% of (i) non-stabilised and (ii) 3 mol% yttria-stabilised zirconia, respectively, were investigated. XRD analyses revealed that the texture degree decreased with increasing second phase content. Microstructural analysis showed zirconia grains inside the textured alumina grains for contents ≤ 5 vol%, affecting the mode of fracture. Fracture toughness of textured alumina significantly decreased with the addition of a second phase. In the case of non-stabilised zirconia, the constraint of the alumina matrix and the small grain size led to a lower fracture toughness in comparison to monolithic textured alumina (K Ic = 5.1 MPa m1/2). The fracture toughness of textured alumina with 3 mol% yttria-stabilised zirconia was comparable to equiaxed alumina, independent of the content ratio (K Ic = 3.5 MPa m1/2). [ABSTRACT FROM AUTHOR]

Fabrication of 3D-printed ceramic parts with high complexity and high spatial resolution often demands low wall thickness as well as high stiffness at the green state, whereas printing simpler geometries may tolerate thicker, more compliant walls with the advantage of a rapid binder-burn-out and sintering process. In this work, the influence of the binder system on the thermophysical properties of 3D-printed stabilized zirconia ceramics was investigated. Samples were fabricated with the lithography- based ceramic manufacturing (LCM) technology using two different photosensitive ceramic suspensions (LithaCon 3Y230 and LithaCon 3Y210), with the same ZrO2 powder. A significant difference in stiffness in the green state (~3 MPa vs. ~32 MPa for LithaCon 3Y230 and LithaCon 3Y210, respectively) was measured, associated with a rather loose or a linked network formed in the binder due to photopolymerization. Both materials reached high relative densities, that is, >99%, exhibiting a homogeneous fine-grained microstructure. No significant differences on the coefficient of thermal expansion (11.18 ppm/K vs. 11.17 ppm/K) or Young's modulus (207 GPa vs. 205 GPa) were measured, thus demonstrating the potential of tailoring binder systems to achieve the required accuracy in 3D-printed parts, without detrimental effects on material's microstructure and thermophysical properties at the sintered state. [ABSTRACT FROM AUTHOR]

This study aimed to assess the effect of airborne particle abrasion (APA) and regeneration firing (RF) on the subsurface damage and strength distribution of 3D-printed 3Y-TZP and 5Y-PSZ zirconia parts for dental applications. Disc-shaped specimens were prepared using vat photopolymerization (VPP) technology from 3Y and 5Y zirconia ceramics, followed by thermal debinding and sintering. APA treatment with 50 µm Al 2 O 3 particles and RF at 1000 °C for 15 min were applied. Microstructural analysis was conducted using FIB-SEM, and XRD analysis determined crystalline phase content. Biaxial flexural strength was measured using the ball on three balls method and analyzed with Weibull statistics. ANOVA and Tukey HSD test were employed to compare strength differences between groups. APA treatment increased the flexural strength of the 3Y specimens but decreased it for the 5Y specimens. RF treatment reversed the effect, restoring the strength to as-sintered levels for both materials. APA-treated 3Y specimens exhibited characteristic strength values above 1400 MPa, attributed to phase-transformation toughening. As sintered 5Y specimens showed strength values above 600 MPa. APA treatment increased the Weibull modulus of the 5Y specimens, indicating a narrower defect size distribution. The study demonstrates that the impact of APA and RF treatments on the mechanical properties and reliability of VPP-fabricated 3Y-TZP and 5Y-PSZ ceramics is comparable to conventionally prepared zirconia. VPP technology for 3D printing provides a viable approach for future manufacturing of dental restorations with potential clinical applications. • VPP technology enables the fabrication of zirconia ceramics that meet the standards for dental applications. • The strength of VPP-fabricated zirconia ceramics is influenced by airborne particle abrasion and regeneration firing. [ABSTRACT FROM AUTHOR]

In this work, textured ceramics were successfully obtained using press-compaction-assisted binder jetting for the first time. A mixture of alumina nanoplatelets and nanoparticles was used as the feedstock powder (the nanoplatelets served as templates for epitaxial grain growth during sintering while the nanoparticles were consumed by the grain growth). The nanoplatelet fraction in the mixture was varied from 0 wt% to 50 wt%. Green samples were prepared with a lab-designed press-compaction-assisted binder jetting machine. The green samples were then sintered in a furnace and their sintered densities were measured. A scanning electron microscope and X-ray diffractometer were used to investigate the degree of texture in the sintered samples. Finally, the biaxial flexural strength of the sintered samples was measured. As the nanoplatelet fraction increased, the sintered density decreased, but the degree of texture increased. Interestingly, the biaxial flexural strength of the sintered samples with 5 wt% or 10 wt% nanoplatelets was higher than those without nanoplatelets, suggesting the increased degree of texture has a stronger effect on the mechanical response than the reduced sintered density under these conditions. [ABSTRACT FROM AUTHOR]

A coupled stress-energy criterion is utilized to predict initiation of both edge and tunnelling cracks in layered ceramics containing thermal residual stresses. Edge (surface) cracks may originate in layers having high compressive in-plane stresses while tunnelling (internal) cracks may form in layers with high tensile in-plane stresses. This work investigates the influence of both the residual stresses magnitude and layer thickness on the formation of surface cracks and provides a design map defining safe regions where no cracks will be present in the sintered multilayer architecture upon reaching the room temperature. Necessary stress and energy inputs to evaluate the coupled criterion are calculated using the finite element method. Simulation results are validated with experimental observations on sample architectures fabricated with layers of various thicknesses and in-plane thermal residual stresses. The good agreement demonstrates the potential of the stress-energy coupled criterion for designing crack-free multi-layered ceramic architectures. [ABSTRACT FROM AUTHOR]

Mimicking the damage tolerance of biological materials such as nacre has been realised in textured layered alumina ceramics, showing improved reliability as well as fracture resistance at room temperature. In this work, the fracture behaviour of alumina ceramics with textured microstructure and laminates with embedded textured layers are investigated under uniaxial bending tests at elevated temperatures (up to 1200 °C). At temperatures higher than 800 °C monolithic textured alumina favours crack deflection along the basal grain boundaries, corresponding to the transition from brittle to more ductile behaviour. In the case of laminates, the loss of compressive residual stresses is counterbalanced by the textured microstructure, effective up to 1200 °C. This study demonstrates the potential of tailoring microstructure and architecture in ceramics to enhance damage tolerance within a wide range of temperatures. [ABSTRACT FROM AUTHOR]

This work demonstrates how to enhance contact damage resistance of alumina‐based ceramics combining tailored microstructures in a multilayer architecture. The multilayer system designed with textured alumina layers under compressive residual stresses embedded between alumina–zirconia layers was investigated under Hertzian contact loading and compared to the corresponding monolithic reference materials. Critical forces for crack initiation under spherical contact were detected through an acoustic emission system. Damage was assessed by combining cross‐section polishing and ion‐slicing techniques. It was found that a textured microstructure can accommodate the damage below the surface by shear‐driven, quasi‐plastic deformation instead of the classical Hertzian cone cracking observed in equiaxed alumina. In the multilayer system, a combination of both mechanisms, namely Hertzian cone cracking on the top (equiaxed) surface layer and quasi‐plastic deformation within the embedded textured layer, was identified. Further propagation of cone cracks at higher loads was hindered and/or deflected owed to the combined action of the textured microstructure and compressive residual stresses. These findings demonstrate the potential of embedding textured layers as a strategy to enhance the contact damage tolerance in alumina ceramics. [ABSTRACT FROM AUTHOR]

The quality of crystallographic alignment in textured ceramics produced by tape casting and templated grain growth (TGG) has been little studied despite its demonstrated impact on magnetic, piezoelectric, and optical properties. Physical and crystallographic alignment of anisotropic template particles is shown to be directly linked to the casting rate, gap height, and casting viscosity during tape casting. These parameters are shown to affect the shape and magnitude of the shear rate profile under the doctor blade during casting which in turn causes a gradient in the torque acting on anisotropic particles. The magnitude of the torque, the time the slurry is exposed to torque during casting, and the ratio of casting height to template diameter are demonstrated to enable the particle alignment process to be tailored to produce well‐aligned template particles. Crystallographic alignment of the textured ceramic was quantified by grain misalignment angle (full width at half maximum, FWHM) and degree of orientation (r) and is directly correlated with the degree of torque during casting. High‐quality alignment (FWHM = 4.5°; r = 0.13) was demonstrated in the model TGG system consisting of submicrometer alumina and 5 vol% 11 μm diameter template platelet particles. [ABSTRACT FROM AUTHOR]