Influence of scanning methods on the forming accuracy and flexural strength of Al 2 O 3 ceramic prepared by laser scanning stereolithography

Additive manufacturing of structural ceramics: a historical perspective

Advanced ceramic materials with complex design have become inseparable from the current engineering applications. Due to the limitation of traditional ceramic processing, ceramic additive manufacturing (AM) which allows high degree of fabrication freedom has gained significant research interest. Among these AM techniques, low-cost robocasting technique is often considered to fabricate complex ceramic components. In this work, aqueous ceramic suspension comprising of commercial nano-sized yttria-stabilized zirconia (YSZ) powder has been developed for robocasting purpose. Both fully and partially stabilized YSZ green bodies with complex morphologies were successfully printed in ambient conditions using relatively low-solid-content ceramic suspensions ( 94% of the theoretical density despite its high linear shrinkage (up to 33%). The microstructure analysis indicated that dense fully and partially stabilized YSZ with grain size as small as 1.40 ± 0.53 and 0.38 ± 0.10 μm can be obtained, respectively. The sintered partially stabilized YSZ solid and porous mesh samples (porosity of macro-pores >45%) exhibited hardness up to 13.29 GPa and flexural strengths up to 242.8 ± 11.4 and 57.3 ± 5.2 MPa, respectively. The aqueous-based ceramic suspension was also demonstrated to be suitable for the fabrication of large YSZ parts with good repeatability.

Ceramics are highly regarded in dental restorations owing to their favorable mechanical properties, chemical resistance, biocompatibility, and aesthetic features. Ceramic additive manufacturing (AM) technology has emerged as a promising solution that offers advantages over traditional techniques such as injection molding, die pressing, tape casting, and milling. Ceramic AM is, however, still under development, with new technologies and devices continuously emerging. This paper provides a comprehensive review of the latest research and applications of ceramic AM in dental restoration, focusing on the progress made within the past five years. Three perspectives are discussed: ceramic AM technologies, commonly used printable ceramic materials, and different types of dental restorations. Among these, vat photopolymerization is the most widely researched and promising AM technology for large-scale applications. ZrO2 remains the primary material used in AM research, whereas crowns and bridges are the most frequently studied and are the closest to industrialized dental restorations. Currently, ceramic AM satisfies the clinical requirements of accuracy, mechanical performance, and biocompatibility. However, compared with traditional methods, it lacks significant advantages in terms of cost and manufacturing efficiency, limiting its large-scale application. Further improvements are necessary in all stages, including raw materials, equipment, post-processing, and standardization.

The additive manufacturing of electro-ceramics is a major technological challenge with many possible applications. The technology can prototype and produce in small volume production, custom dielectric, piezoelectric and solid state ionic devices. Sandia National Laboratories was the birthplace of modern, 3-D ceramic additive manufacturing. The newly developed manufacturing methods are considered to be the foundation of 3-D printing via particulate slurries and our spin off company Robocasting Enterprises, is commercially producing dense ceramic and composite parts. These parts are used in various applications including complex geometry catalyst supports and casting filters. This technique is based on the layer-by-layer deposition of highly loaded colloidal slurries that are extruded through a small nozzle. The rheology of the slurry is crucial in order to maintain the structural integrity of the part being built, as Robocasting does not rely on polymerization reactions or solidification to retain shape after extrusion. Since this process is essentially binderless, a dense ceramic part can typically be freeformed, dried, and sintered in less than 24 hours. Although Robocasting is a highly useful technique, it has been optimized for ceramic and composite materials. More recently there has been some work on expanding this technology for use in printing electrode materials. Printing conductors and other structures for electrochemical and electronics using direct write technology gives the potential to reduce production time and reduce waste of expensive material. We have demonstrated that this direct write manufacturing technique can produce Multi-Chip Modules (MCM) by depositing silver and gold on Low Temperature Co-fired Ceramics (LTCC). We have also applied this additive manufacturing technique to our unique design of electrochemical gas sensors. These multi-component mixed potential sensors consist of solid electrodes and a porous electrolyte. In order to expand the versatility of this manufacturing method to be used in solid state ionic devices, slurries of solid electrolytes and electrode materials with specific rheological properties were developed. Another challenge was controlling the residual stress and shrinkage through the material properties of various components. These devices are capable of detecting NOx, hydrocarbons, and NH3 at concentrations on the order of parts per million. The additive manufacturing technique allows for the rapid prototyping of these devices and low volume production of custom devices optimized for specific applications. Figure 1

Research in the field of ceramic additive manufacturing (AM) has been rapidly accelerating, resulting in hundreds of publications and review articles in recent years. While strides have been made in forming near‐net and complex‐shaped ceramic components, challenges remain that inhibit more widespread implementation. In this perspective, we provide a meta‐analysis of recent review articles and highlight a deficiency in two areas of promising future directions to address remaining challenges. The first is incorporation of fiber reinforcements in printed parts to overcome the challenges of poor mechanical performance of monolithic ceramics. Recent work in the area has shown promise incorporating discrete fiber reinforcements as an easier use case given existing equipment limitations, but continuous fibers are needed to reach full toughness potential. Here, we overview some options and future directions bases on success in polymer composites. Second, artificial intelligence (AI) approaches, including machine learning (ML), are suggested in order to accelerate feedstock development and process optimization. While there has been very limited work to date in utilizing AI/ML techniques for ceramic AM, again inspiration and lessons learned are drawn from the polymer AM community.

Rapid and flexible manufacturing of good-quality ceramic parts is desirable in many fields, but is still challenging. Conventional methods often require expensive molds and/or difficult machining processes, while most of the additive manufacturing (AM) methods utilize binders and thus need additional debinding step(s) that can be very time-consuming and/or cause quality problems. Laser powder bed fusion (LPBF) with full melting of ceramic powder is the major AM method that has the potential to manufacture highly densified ceramic parts in complex shapes largely in a single step. However, it still frequently suffers from cracks, rough surfaces, insufficient densification, and/or balling, often due to three challenges difficult to address simultaneously: (1) high gradient of temperature, (2) inadequate powder melting, and (3) an overlarge melt pool. This paper reports a preliminary study of a novel ceramic AM process: pulsed-continuous dual-beam laser powder bed fusion, which has demonstrated promising performance under the conditions studied. The fundamental mechanisms for the experimental results have been analyzed based on proposed hypotheses for the novel ceramic AM process. One of the hypotheses has been preliminarily tested using a thermal model. The study shows that this novel ceramic AM process has a great potential to address all of the aforementioned three challenges faced by LPBF of ceramics to help provide an ideal method for flexible and rapid manufacturing of high-quality ceramic parts. Lots of future work on the novel process is still needed.

Compared with silicon-based power devices, wide bandgap (WBG) semiconductor devices operate at significantly higher power densities required in applications, such as electric vehicles and more electric airplanes. This necessitates the development of power electronics packages with enhanced thermal characteristics that fulfill the electrical insulation requirements. The present research investigates the feasibility of using ceramic additive manufacturing (AM), also known as three-dimensional (3-D) printing, to address thermal and electrical requirements in packaging gallium nitride (GaN)-based high-electron-mobility transistors (HEMTs). The goal is to exploit design freedom and manufacturing flexibility provided by ceramic AM to fabricate power device packages with a lower junction-to-ambient thermal resistance ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$R_{\theta \text {JA}}$ </tex-math></inline-formula> ). Ceramic AM also enables incorporation of intricate 3-D features into the package structure in order to control the isolation distance between the package source and drain contact pads. Moreover, AM allows to fabricate different parts of the packaging assembly as a single structure to avoid high thermal resistance interfaces. For example, the ceramic package and the ceramic heatsink can be printed as a single part without any bonding layer. Thermal simulations under different thermal loading and cooling conditions show the improvement of thermal performance of the package fabricated by ceramic AM. If assisted by an efficient cooling strategy, the proposed package has the potential to reduce <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$R_{\theta \text {JA}}$ </tex-math></inline-formula> by up to 48%. The results of the preliminary efforts to fabricate the ceramic package by AM are presented, and the challenges that have to be overcome for further development of this manufacturing method are recognized and discussed.

Ceramic additive manufacturing and microstructural analysis of tricalcium phosphate implants using X-ray microcomputed tomography

Vat photopolymerization is characterized by its high precision and efficiency, making it a highly promising technique in ceramic additive manufacturing. However, the process faces a significant challenge in the form of recoating defects, necessitating real-time monitoring to maintain process stability. This article presents a defect detection method that leverages multi-image fusion and deep learning for identifying recoating defects in ceramic additive manufacturing. In the image fusion process, multiple single-channel recoating images captured by monitoring camera positioned near the photopolymerization equipment are merged with curing area mask image to create a three-channel color image. The recoating images suffer from perspective distortion due to their side view. To facilitate fusion with the curing area image, image rectification technique is applied to correct the perspective distortion, transforming the side view recoating images into a top-down view. Subsequently, the fused images are processed using a channel-wise YOLO (You Only Look Once, CW-YOLO) method to extract features, enabling the distinction of various types of defects. When compared with other deep learning models, CW-YOLO achieves higher detection accuracy while maintaining a detection rate of 103.58fps, meeting the requirements for real-time detection. Furthermore, the paper introduces the F1 score as a comprehensive evaluation metric, capturing both detection accuracy and recall rate. The results show that the F1 score is enhanced by approximately 10% after image fusion, demonstrating that the proposed method can significantly improve defect detection, particularly in cases involving difficult-to-distinguish defects like material shortages and scratches.

Ceramic additive manufacturing (C-AM) is highlighted as a technology that can overcome the inherent limitations of ceramics such as processability and formability. This process creates a structure by slicing a 3D model and stacking ceramic materials layer-by-layer without mold or machining. C-AM is a technology suitable for the era of multiple low-volume because it is more flexible than conventional methods for shape complexity and design modification. However, many barriers to practical use remain due to process speed, defects, and lack of knowledge. This review focuses on studies to overcome the limitations of C-AM in terms of process and materials. The C-AM process has been advanced through various studies such as model/equation-based parameter control and high-speed sintering using external energy. Besides, by improving and fusing existing technologies, high-precision high-speed printing technology has been improved. A variety of material studies have been made of manufacturing ceramic structures with superior properties using preceramic polymers and composite materials. Through these studies, C-AM has been applied to various fields such as medicine, energy, environment, machinery, and architecture. These continued growths and diverse results demonstrate the importance and potential of C-AM based ceramic manufacturing technology.

Additive manufacturing (AM) offers the unique capability of directly creating three-dimensional complicated ceramic components with high process flexibility and outstanding geometry controllability. However, current ceramic AM technology is mainly limited to the creation of a single material, which falls short of meeting the multiple functional requirements under increasingly harsh service circumstances. Ceramic multi-material additive manufacturing (MMAM) technology has great potential for integrally producing multi-dimensional multi-functional components, allowing for point-by-point precision manufacturing of programmable performance/functions. However, there is a huge gap between the capabilities of the existing ceramic MMAM technology and the requirements for industrial application. In this review, we discuss and summarize the research status of ceramic MMAM technology from the perspectives of feedstock selection, printing process, post-processing, component performance, and application. Throughout the discussion, the challenges associated with ceramic MMAM such as heterogeneous material coupled printing, heterogeneous interfacial bonding, and co-sintering densification have been put forward. This review aims to bridge the gap between AM technologies and the requirements for multifunctional ceramic components by analyzing the existing limitations in ceramic MMAM and pointing out future needs.

Phase formation in silicon nitride based ceramics after post-sintering heat treatment: V.A.Ijevskii. Poroskovaya Metall., no 9/10, 1996, 64–74. (In Russian.)

CerAMfacturing of silicon nitride by using lithography-based ceramic vat photopolymerization (CerAM VPP)

Additive manufacturing (AM) represents a set of manufacturing processes that create complex 3D parts out of polymers, metals, and ceramics. AM of metals and ceramics is widely used to produce parts for aerospace, automotive, and medical applications. At the micro- and nano-scales, AM is poised to become the enabling technology for efficient 3D microelectromechanical systems (MEMS), 3D micro-battery electrodes, 3D electrically small antennae, micro-optical components, and photonics. Today, the minimum feature size for most commercially available metal and ceramic AM is limited to ~20-50 μm. Currently, no established processes can reliably produce complex 3D metal and ceramic parts with sub-micron features. In this thesis, we first demonstrate a nanoscale metal AM process that can produce ~300 nm features out of nanocrystalline, nanoporous nickel using synthesized hybrid organic-inorganic materials, two-photon lithography, and pyrolysis. We study microstructure and mechanical properties of as-fabricated nickel architectures and compare their structural strength to established AM processes. We then show how this process can be extended to other metals and metalloids, including Mg, Ge, Si, and Ti. This study extends further into nanoscale AM of transparent, high refractive index materials for micro-optics and photonic crystals. We develop an AM process to 3D print fully dense nanocrystalline rutile titanium dioxide (TiO₂) with feature dimensions down to ~120 nm. We carefully study and model the relationship between feature dimensions and process parameters to achieve a Finally, a microscale AM process of titanium dioxide is demonstrated for photocatalytic water treatment. We show how synthesized hybrid organic-inorganic materials can be applied for stereolithography to print TiO₂ architectures with 100 μm features. We use the developed 3D printing process to investigate the effect of 3D architecture on the efficiency of photocatalytic water treatment. This work establishes a versatile and efficient pathway to create three-dimensional nano-architected metals and ceramics and to investigate their properties for applications in 3D MEMS, micro-optics, photonics, and photocatalysis.

The present decade has witnessed a huge volume of research revolving around a number of Additive Manufacturing (AM) techniques, especially for the fabrication of different metallic materials. However, fabrication of ceramics and cermets using AM-based techniques mainly suffers from two primary limitations which are: (i) low density and (ii) poor mechanical properties of the final components. Although there has been a considerable volume of work on AM based techniques for manufacturing ceramic and cermet parts with enhanced densities and improved mechanical properties, however, there is limited understanding on the correlation of microstructure of AM-based ceramic and cermet components with the mechanical properties. The present article is aimed to review some of the most commonly used AM techniques for the fabrication of ceramics and cermets. This has been followed by a brief discussion on the microstructural developments during different AM-based techniques. In addition, an overview of the challenges and future perspectives, mainly associated with the necessity towards developing a systematic structure-property correlation in these materials has been provided based on three factors viz. the efficiency of different AM-based fabrication techniques (involved in ceramic and cermet research), an interdisciplinary research combining ceramic research with microstructural engineering and commercialisation of different AM techniques based on the authors’ viewpoints.