3D printing of complex shaped alumina parts

Alpha-alumina powder was mixed with methyl cellulose as a binder with concentration as low as 0.25% by weight in an aquoes medium and kneaded in a high shear mixer to obtain a printable paste. The paste was subjected to rheological measurements and exhibited a shear rate exponent of 0.54 signifying the shear thinning behavior. The paste was used for printing parts with various shapes according to CAD model by employing a ram type 3D printer. Printed parts were dried and the green density was determined. Further, the parts were also subjected to X-ray radiography in order to evaluate the possible occurrence of printing defects. The samples were sintered under pressureless condition at 1650?°C in a muffle furnace and Hot Isostsically Pressed (HIP) at 1350?°C and a pressure of 1650?bar using a vacuum encapsulated SS CAN. Hot Isostatic pressing resulted in a higher density of 3.94?g/cc in comparison to 3.88?g/cc obtained under pressureless conditions and also shown superior mechanical properties. HIPing of 3D printed samples not only resulted in possible healing of printing defects as reavealed by X-ray radiography but also enhanced the diffusion at low temperature of 1350?°C leading to finer grain sizes as complemented by the microstructure.     

Fabrication of complex shaped alumina parts by gelcasting on 3D printed moulds

Alumina ceramic components were produced using gelcasting and 3D printing techniques to generate the end product. The 3D printed mould made from (acrylonitrile butadiene styrene) ABS filament provides a convenient demoulding method by dissolution of the mould using acetone as a solvent. This process enables low cost production of complex shaped ceramic components. The effect of the suspension solid loading on the properties and microstructure of complex shaped alumina parts was investigated. The produced ceramic components had densities up to 99.0%, hardness of 18 GPa, flexural strength of 374 MPa and a fracture toughness of 3.8 MPa√m after sintering in air for 3 h, in good agreement with published values.     

Enhanced mechanical properties of 3D printed alumina ceramics by using sintering aids

Stereolithography based 3D printing provides an efficient pathway to fabricate alumina ceramics, and the exploration on the mechanical properties of 3D printed alumina ceramics is crucial to the development of 3D printing ceramic technology. However, alumina ceramics are difficult to sinter due to their high melting point. In this work, alumina ceramics were prepared via stereolithography based 3D printing technology, and the improvement in the mechanical properties was investigated based on the content, the type and the particle size of sintering aids (TiO₂, CaCO₃, and MgO). The flexural strength of the sintered ceramics increased greatly (from 139.2 MPa to 216.7 MPa) with the increase in TiO₂ content (from 0.5 wt% to 1.5 wt%), while significant anisotropy in mechanical properties (216.7 MPa in X-Z plane and 121.0 MPa in X–Y plane) was observed for the ceramics with the addition of 1.5 wt TiO₂. The shrinkage and flexural strength of the ceramics decreased with the increase in CaCO₃ content due to the formation of elongated grains, which led to the formation of large-sized residual pores in the ceramics. The addition of MgO help decrease the anisotropic differences in shrinkage and flexural strength of the sintered ceramics due to the formation of regularly shaped grains. This work provides guidance on the adjustment in flexural strength, shrinkage, and anisotropic behavior of 3D printed alumina ceramics, and provides new methods for the fabrication of 3D printed alumina ceramics with superior mechanical properties.     

Silica strengthened alumina ceramic cores prepared by 3D printing

Ceramic cores based on alumina and silica are important in the manufacturing of hollow blades. However, obtaining good properties and precision is still challenging. In this research, alumina-based ceramics cores were obtained by 3D printing technology, and the effects of silica contents on the mechanical properties of the as-obtained alumina ceramic cores were evaluated. The results showed significant improvements in flexural strengths of the ceramics from 13.3 MPa to 46.3 MPa at silica contents from 0 wt% to 30 wt% due to formation of mullite phase (Al₆Si₂O₁₃). By contrast, the flexural strengths declined as silica content further increased due to the generation of massive liquid phase. Also, porous structures and cracks were observed by scanning electron microscopy due to the removal of cured photosensitive resin and the mullitization reaction between alumina and silica, respectively. The manufacturing process of hollow blades required ceramic cores with flexural strengths greater than 20 MPa to resist the strike of metal liquid, as well as open porosity above 20 % to provide space for alkali liquor to dissolve the ceramic cores. As a result, 10 wt% silica was determined as the optimal value to yield ceramics with improved properties in terms of flexural strength (35.6 MPa) and open porosity (47.5 %), thereby satisfy the application requirement for the fabrication of ceramic cores.     

Fabrication of alumina ceramics with functional gradient structures by digital light processing 3D printing technology

Alumina ceramics with different unit numbers and gradient modes were prepared by digital light processing (DLP) 3D printing technology. The side length of each functional gradient structure was 10 mm, the porosity ratio was controlled to 70%, and the number of units were (1 × 1 × 1 unit) and (2 × 2 × 2 unit) respectively. The different gradient modes were named FCC, GFCC-1, GFCC-2 and GFCC-3. SEM, XRD, and other characterization methods proved that these gradient structures of alumina ceramics had only α-Al2O3 phase and good surface morphology. The mechanical properties and energy absorption properties of alumina ceramics with different functional gradient structures were studied by compression test. The results show that the gradient structure with 1 × 1 × 1 unit has better mechanical properties and energy absorption properties when the number of units is different. When the number of units is the same, GFCC-2 and GFCC-3 gradient structures have better compressive performance and energy absorption potential than FCC structures. The GFCC-2 gradient structure with 1 × 1 × 1 unit has a maximum compressive strength of 19.62 MPa and a maximum energy absorption value of 2.72 × 105 J/m3. The good performance of such functional gradient structures can provide new ideas for the design of lightweight and compressive energy absorption structures in the future.     

3D printed polylactide-based zirconia-toughened alumina composites: fabrication,mechanical, and in vitro evaluation

Fused deposition modeling (FDM) has been a commonly used technique in the fabrication of geometrically complex biodegradable scaffolds for bone tissue engineering. Generally, either individual polylactide (PLA) or its combination with calcium phosphates or bioglass has been employed to design scaffolds through the principles of FDM. In this study, FDM protocol has been employed to design 3D printed PLA/zirconia-toughened alumina (ZTA). A series of PLA/ZTA combinations have been attempted to determine the feasibility of the resultant in filament extrusion and their subsequent capacity to obtain a stable 3D printed component. A maximum of 80 wt.% PLA and 20 wt.% ZTA has been determined as an optimum combination to yield a stable 3D structure beyond which an enhanced ZTA content in the PLA matrix yielded a fragile filament that lacked effectiveness in 3D printing. 5 and 10 wt.% of ZTA addition in the PLA matrix produced a better 3D design that reasonably displayed good mechanical properties. Depending on the ceramic content, a homogeneous dispersion of the constituent elements representative of ZTA has been determined throughout the PLA matrix. Simulation studies through finite element analysis (FEA) exhibited good corroboration with the test results obtained from the mechanical studies.     

3D gel printing of alumina ceramics followed by efficient multi-step liquid desiccant drying

Dense alumina ceramics were additively manufactured efficiently through a 3D gel printing process. Hydroxyethyl cellulose (HEC) was applied to ensure the printability and rigid of the gel made from boehmite. A multi-step liquid desiccant drying method was implemented to improve the drying efficiency. The results showed that the solid loading and HEC addition were two useful parameters for adjusting the rheology properties of the gel to make it suitable for 3D printing. With polyethylene glycol(PEG) added as liquid desiccants, the printed bodies with section size of 10 mm could be dried within 26 h during which the deformation and crack formation was avoided despite a high linear shrinkage of 45 % was encountered. The successful preparation of dense monolithic alumna ceramics parts with an average grain size of 1 μm, 99 % of the theoretical density and a flexural strength of 380 ± 45 MPa indicated the potential of this process.     

Transparent alumina ceramics fabricated by 3D printing and vacuum sintering

Transparent alumina ceramics were fabricated using an extrusion-based 3D printer and post-processing steps including debinding, vacuum sintering, and polishing. Printable slurry recipes and 3D printing parameters were optimized to fabricate quality green bodies of varying shapes and sizes. Two-step vacuum sintering profiles were found to increase density while reducing grain size and thus improving the transparency of the sintered alumina ceramics over single-step sintering profiles. The 3D printed and two-step vacuum sintered alumina ceramics achieved greater than 99 % relative density and total transmittance values of about 70 % at 800 nm and above, which was comparable to that of conventional CIP processed alumina ceramics. This demonstrates the capability of 3D printing to compete with conventional transparent ceramic forming methods along with the additional benefit of freedom of design and production of complex shapes.     

3D printing of fine alumina powders by binder jetting

Additive manufacturing of ceramics is still at an early-development stage; however, the huge interest in custom production of these materials has led to the development of different techniques that could provide highly performing devices. In this work, alumina (α-Al₂O₃) components were produced by binder jetting 3D printing (BJ), a powder-based technique that enables the ex-situ thermal treatment of the printed parts. The employment of fine particles has led to high green relative density values (>60 %), as predicted by Lubachevsky-Stillinger algorithm and DEM modelling. Then, extended sintering has been observed on samples treated at 1750 °C that have reached a final density of 75.4 %. Finally, the mechanical properties of the sintered material have been assessed through bending test for flexural resistance and micro-indentation for Vickers hardness evaluation.     

Heat dissipation in 3D printed cellular aluminum nitride structures

The improvement of heat dissipation in electronic and energy devices is a challenge that can be addressed through the use of highly porous materials. Presently, the additive manufacturing of 3D aluminum nitride is described, and different lattice patterns with porosities in the range 45–64 % are achieved by direct ink writing. All the structures are robust and the effective thermal conductivity (k_eff) for cuboid structures decreases by 50–75 % with the filament separation and shows anisotropic characteristics, since k_eff along the longitudinal axis of the scaffold is up to six times greater than for the transversal one. Heat transfer during free cooling experiments for cuboid and cylinder scaffolds, after rapid heating at temperatures above 1000 °C, takes place by radiation for temperatures >500 °C and by convection through the complete cooling process. The heat dissipation time constants of both processes decrease almost linearly with the designed scaffold parameters of porosity and rod separation.     

Effect of the nanoparticles on the morphology and mechanical performance of thermally blown 3D printed HIPS foams

Cellular polymer nanocomposites can combine high mechanical performance with low density. However, the manufacturing of porous nanocomposites into complex shapes can represent a challenge. Therefore, this article deals with the preparation, characterization, and 3D printing of porous nanocomposites. The filaments were extruded from the polymer nanocomposite filled by thermal chemical blowing agent, and then processed by 3D printing into the required shapes. In-situ and post-treatment foaming strategies were investigated and compared. The nanoparticles (NPs) significantly affected the processing, structure, thermal and mechanical properties of polymeric foams. The NPs, serving as a nucleating agent, allowed preparation of smaller pores and led to finer and more homogeneous foams. At the same time, they reinforced foam walls and thus improved mechanical properties. Moreover, NPs catalyzed decomposition of the blowing agent grains at lower temperature which brought about faster and more efficient foaming. This study showed the straightforward approach to prepare mechanically robust lightweight 3D printed materials.     

Preparation of Si3N4 ceramic based on digital light processing 3D printing and precursor infiltration and pyrolysis

The emergence of digital light processing (DLP) 3D printing technology creates favorable conditions for the preparation of complex structure silicon nitride (Si₃N₄) ceramics. However, the introduction of photosensitive resin also makes the Si₃N₄ ceramics prepared by 3D printing have low density and poor mechanical properties. In this study, high-density Si₃N₄ ceramics were prepared at low temperatures by combining DLP 3D printing with precursor infiltration and pyrolysis (PIP). The Si₃N₄ photocurable slurry with high solid content and high stability was prepared based on the optimal design of slurry components. Si₃N₄ green parts were successfully printed and formed by setting appropriate printing parameters. The debinding process of printed green parts was further studied, and the results showed that samples without defects and obvious deformation can be obtained by setting the heating rate at .1°C/min. The effect of the PIP cycle on the microstructure and mechanical properties of the Si₃N₄ ceramics was studied. The experimental results showed that the mass change and open porosity of the samples tended to be stable after eight PIP cycles, and the open porosity, density, and bending strength of the Si₃N₄ ceramics were 1.30% (reduced by 97%), 2.64 g/cm³ (increased by 43.5%), and 162.35 MPa.     

（急）3D打印气凝胶的研究现状

气凝胶材料具有高比表面积、高孔隙率、低密度以及低热导率等诸多优良性能，被认为是21世纪的十大新材料之一。然而传统气凝胶由于其力学性能有限，难以经过后加工技术形成所需的复杂形状结构，满足实际应用的需求。因此，无需复杂后处理即定制化制备复杂形状结构材料的3D打印技术有望成为突破气凝胶材料应用瓶颈的先进制造技术。本文从3D打印气凝胶的技术种类和材料类型两个方面，综述了3D打印气凝胶材料的研究进展；归纳了3D打印气凝胶材料在阻燃隔热、介电和组织工程中的独特应用并展望了3D打印气凝胶的发展趋势。最后指出扩宽3D气凝胶材料的材料体系、开发更适应气凝胶打印的3D打印技术、提升打印精度与速度和深入研究3D打印气凝胶的可控孔隙结构对其性能的影响是未来的几个重要的研究方向。3D打印气凝胶材料的开发有望促进气凝胶材料的快速发展。     

3D打印用光敏树脂材料研究进展

主要介绍了3D打印用光敏树脂的研究进展,包括为提高打印件性能而进行的光敏树脂的改性的研究现状,以及光敏树脂的电学、热学、生物医药等方面的功能化研究,最后对3D打印光敏树脂的发展做出总结及展望。     

Fracture and mechanical properties of lightweight alumina ceramics prepared by fused filament fabrication

Fused filament fabrication (FFF), as one of the additive manufacturing technology, provides cost-effective and relatively fast preparation of 3D objects of desired dimensions and design. In this work, a composite filament containing 50 vol. % of sub-micron alumina powder was successfully used for the manufacturing of samples with prismatic design. The influence of the layer thickness (0.1–0.3 mm) on the final bulk density and mechanical properties were investigated. Sintering at 1600 °C for 1 h results in relative densities ranging from 80 to 89 % and the flexural strength reached 200–300 MPa depending on the layer thickness used for the printing.     

On reducing anisotropy in 3D printed polymers via ionizing radiation

The mechanical properties of materials printed using fused filament fabrication (FFF) 3D printers typically rely only on adhesion among melt processed thermoplastic polymer strands. This dramatically limits the utility of FFF systems today for a host of manufacturing and consumer products and severely limits the toughness in 3D printed shape memory polymers. To improve the interlayer adhesion in 3D printed parts, we introduce crosslinks among the polymer chains by exposing 3D printed copolymer blends to ionizing radiation to strengthen the parts and reduce anisotropy. A series polymers blended with specific radiation sensitizers, such as trimethylolpropane triacrylate (TMPTA) and triallyisocyanurate (TAIC), were prepared and irradiated by gamma rays. Differential scanning calorimetry (DSC), tensile testing, dynamic mechanical analysis (DMA) and attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) were employed to characterize the thermomechanical properties and the chemical structure of the various polymers. TAIC was shown to be a very effective radiation sensitizer for 3D printed sensitized polylactic acid (PLA). The results further revealed that crosslinks induced by radiation temperatures near T_g of shape memory systems have prominently enhanced the thermomechanical properties of the 3D printed polymers, as well as the solvent resistance. This enables us to deliver a new generation of inexpensive 3D printable, crosslinked parts with robust thermomechanical properties.     

Mechanical,electrical and thermal performance of hybrid polyethylene-graphene nanoplatelets-polypyrrole composites: a comparative analysis of 3D printed and compression molded samples

ABSTRACT

The paper focuses on the investigation of the 3D printing of multi-functional composites using graphene nanoplatelets (GNP), polypyrrole (PPY) and linear low-density polyethylene (LLDPE). A holistic approach was performed and characterization methods to assess the properties of 3D printed composites and compared with those of compression molded composites and neat LLDPE to understand the factors affecting their performance. It has been noted that the 3D printed composites have superior mechanical and electrical properties than neat LLDPE, but slightly lower compared to those of compression molded composites having high packing density of fillers. The nominal increases were 13.2% (tensile strength), 31.9% (flexural strength), 29.4% (flexural modulus) and 24.7% (storage modulus).     

Effect of particle size on mechanical properties of alumina ceramic processed by photosensitive binder jetting with powder spattering technique

As an Additive Manufacturing technique, Binder Jetting enables the fabrication of customized and complex ceramic parts. However, the insufficiency of powder packing in green parts restricts the final products’ densifications and strengths. To form a layer of ceramic green parts, Photosensitive Binder Jetting with powder spattering technique provides entrapment of ceramic powder by printing of photo-curable resin and recoating by releasing the powder through a vibrating mesh. This recoating technique enables the processing of fine alumina powders, the average particle sizes of which are 3 μm, 1.65 μm, and their mixtures. Apparent densities, porosities, mechanical properties, and microstructures of the sintered parts were investigated. The alumina sample with the apparent density of 3.70 g/cm³, the compressive strength of 94.87 MPa, the biaxial strength of 50.06 MPa, and the porosity of 41.01 % was attained by the mixture with 70:30 wt.% of the 3 μm and 1.65 μm powders respectively.     

3D打印凹凸棒土改性光敏树脂制备及力学性能

采用硅烷偶联剂KH550接枝改性凹凸棒土,通过超声分散和3D打印技术进一步制备了有机凹凸棒土/光敏树脂复合物。采用傅里叶变换红外光谱对改性前后的凹凸棒土结构进行了表征;通过拉伸强度和冲击强度试验对复合光敏树脂的力学性能进行了研究;采用扫描电镜观察了复合树脂冲击断面的形貌和改性凹凸棒土在树脂中的分散情况。结果表明:改性凹凸棒土的加入有助于光敏树脂韧性的提高,当添加质量分数3%时,复合光敏树脂的冲击强度最佳。