Additive Manufacturing of Ceramics and Ceramic-Based Composites: Processing, Properties, and Engineering Applications

Additive manufacturing (AM) technologies based on sintering, such as Powder Bed Fusion (PBF), Direct Energy Deposition (DED), Binder Jetting (BJT), and Material Extrusion (MEX), enable the production of complex metallic components with reduced material waste and design flexibility. However, the intrinsic porosity, microstructural anisotropy, and mechanical properties of sintered AM metals significantly influence their machinability, affecting tool wear, surface integrity, and cutting forces. This review explores the key material characteristics affecting the machining performance of sintered AM metals, focusing on conventional processes such as turning, milling, and drilling. The impact of microstructure, density, and mechanical properties on machining outcomes is analyzed, along with the challenges posed by the unique properties of sintered materials. Additionally, post-processing strategies, including heat treatments and surface finishing techniques, are discussed as potential solutions to enhance machinability. The review concludes by identifying future research opportunities, particularly in optimizing AM process parameters and developing hybrid manufacturing approaches to improve the industrial applicability of sintered AM metallic materials. Although previous studies focus on individual AM technologies, this review takes a novel approach by systematically comparing the machinability of metallic materials produced via PBF, DED, BJT, and MEX. By identifying commonalities and differences among these sintering-based AM processes, this work provides a comprehensive perspective on their machining behavior and post-processing requirements, offering valuable insights for industrial applications.

Additive manufacturing (AM) enables the rapid fabrication of parts with complex geometries that cannot be easily manufactured with traditional methods. While originally limited to rapid prototyping, recent advances in AM technology also enable direct fabrication of functional end-use parts in, e.g., aerospace, medical devices, and military applications. However, the transition from rapid prototyping to fabricating end-use parts has also revealed technology barriers, including surface quality, accuracy, part variability, and uncertainty about the process–structure–property relationship, to name a few. Crucially, fundamental questions about friction, wear, and lubrication of AM parts have led to substantial research interest in the tribology community. This Special Issue provides significant value to the tribology community by highlighting recent advances of tribology research related to AM, defining the state-of-the-art of tribology knowledge, and framing the challenges and opportunities for future tribology research in this exciting field. It is a collection of 17 research/review papers covering a wide range of state-of-the-art topics in the tribology of additive manufacturing. All the papers have undergone a rigorous and anonymous peer-review process.Additive manufacturing technology is rapidly progressing and the future may bring many new printing methodologies. However, at present, the AM technology can be broadly grouped into seven categories: binder jetting (BJ), direct energy deposition (DED), material extrusion (ME), material jetting (MJ), powder bed fusion (PBF), sheet lamination, and vat polymerization (VP). Of particular interest is the understanding of the Process–Microstructure–Tribology (PMT) "research hotspot." Table 1 summarizes the topics covered in this Special Issue, in addition to the AM technology and the materials. Furthermore, we categorize the papers into PMT, tribology design, and surface characterization, based on the main topic of the paper. To set the stage, we summarize the contents of the papers per Table 1.Renner et al. presented a review paper focusing on the corrosion and wear properties of AM-fabricated alloys including steel, titanium, and aluminum. The paper points out that AM-fabricated alloys have better corrosion and wear properties than the casted parts, while the influence of process parameters on the microstructures does not hold true across different additive manufacturing processes and materials. Many other challenges—e.g., anisotropic behaviors, effects of heat treatments, the role of nano-particles, and failure analysis—are recommended for future studies in the field. Also noteworthy is the AM-fabricated metal parts (including PBF and DED) often end up with unique microstructures due to the rapid and repeated heating/cooling cycles and extremely large thermal gradient. Indeed, melting and solidification are highly time dependent and complex processes, making it difficult to simulate and predict. These are areas where more research is needed.Sharma et al. presented a literature review on hybrid surface metal matrix composites produced by friction stir processing and provided insight into the PMT relationship. Kang et al. studied the microstructure on the surface, sub-surface, and inner region of a commercial pure Ti part fabricated using laser PBF (LPBF). They indicated that the friction and wear behavior of the three regions are distinct. This is thought to be the consequence of the intrinsic heat treatment induced by the LPBF process. The remelting/heating and recrystallization cause microstructure coarsening and refinement between the three regions.Thasleem et al. studied the influence of various post-processing methods such as heat treatment and electric discharge alloying (EDA) on ambient and elevated temperature wear behavior of LPBF AlSi10Mg alloy and compared with the cast parts. Their results indicated that an EDA-treated part has the least wear-rate and coefficient of friction at both ambient and elevated temperatures due to its higher hardness than other samples. Thus, EDA-treating can be considered as a potential post-processing technique.Microstructure reinforcement is also an efficient way to increase wear resistance. Wang et al. studied the effect of TiB2 content on the microstructure and wear behavior of nano-TiB2p/2024Al composites fabricated by laser DED. Their results revealed that the wear-rate of an 8 wt% TiB2p/2024Al matrix composite with full equiaxed grains is almost 20 times lower than that of the unreinforced alloy due to the grain morphology-induced wear mechanism. Li et al. fabricated a dense Al–Fe–Cr quasicrystal reinforced Al matrix composite using DED. The reinforcement phases contributed to the mechanical mixing layer formation that significantly reduced the coefficient of friction and improved the wear resistance. Luo et al. fabricated short carbon fiber-reinforced nylon using ME and reported that the tribological performance improved.Rolling contact fatigue (RCF) is another critical performance for many tribological applications. Xie et al. and Fasihi et al. used laser cladding to enhance the railway rail materials. They showed that by carefully selecting cladding materials, both wear and RCF performance can be improved. However, micro-cracks may initiate from the interface between clad and unclad regions. Jalalahmadi et al. presented a predictive platform for fatigue prediction and AM-fabricated metallic parts qualification. They reported developing an integrated computational materials engineering tool that includes models of crack initiation and damage progression, exploring the design space across geometries and materials.Additive manufacturing can also be used to design and process unique functional structures, which may create some breakthroughs in tribological design. Suh highlighted the importance of design in improving the performance of all tribological systems. AM was mentioned as an innovative way to produce a part that is very difficult or even impossible to manufacture using conventional manufacturing while at the same time improve the design quality.There is a large body of tribology literature on the use of surface texturing to reduce the friction and wear characteristics of conventional materials. Surface texturing appears to offer viable flexibility for improving the tribological behavior of AM parts as well. Luo et al. reported that by designing specific surface textures—such as convex squares and triangles, processed via ME—they were able to improve the tribological performance. Hoskins and Zou designed and fabricated a micro-texture inspired by Ocellated Skink using two-photon polymerization (TPP), a VP technique producing nanostructures. They reported that wear was substantially reduced due to the texture through the controlled formation of microcracking. Maddox et al. also used TPP to design and fabricate surfaces inspired by frog toes and applied in the piston ring and liner interface. These designs reduce surface friction by an average of 18% and up to 39%, compared to a flat control. Zhang et al. used VP technology to produce various polygonal three-dimensional patterns inspired by dragonfly wings to identify how the polygonal patterns of the samples with bionic wing veins affected the skin friction. Their study provides insight into the mechanism of flow separation of the dragonfly wing and further improves the structure design. Murashima et al. used VP to design and produce a novel morphing surface that selectively performs as a low-friction or break-like surface. By applying air pressure, the surface switches between a convex and a concave shape, giving a different coefficient of friction. It is worth noting that AM of a part often tends to change a "continuous surface" into many discrete layer boundaries, inducing staircase effects due to the layer-on-layer nature. Narasimharaju et al. systematically investigated the impact of varying surface inclination angles on the build direction on the resultant surface textures. The areal surface texture characterization and particle analysis indicated that the resulted surface topographies are strongly correlated with the surface inclination angles.Modeling and simulations of the hydrodynamic effects associated with AM processes are also worth investigating. Wagner and Higgs studied the capillary and hydrodynamic effects of the interfacial flow responsible for primitive formation when the binder spreads into the powder bed and forms a bound network of wetted particles in the BJ process.The collection of articles in this Special Issue represents the active and diverse research efforts in the tribology of additive manufacturing. However, there is still a long way to go in this journey. Fundamental material research, application-oriented research, and novel tribological design are extremely worthwhile and exciting to pursue. We hope this Special Issue on the latest advancements in tribology of additive manufacturing provides insights and stimulates the generation of novel ideas with industrial applications on system diagnosis and machine design for years to come.Finally, we wish to take this opportunity to sincerely thank all the authors for their scientific contributions. Special thanks also to reviewers for their constructive and insightful comments on all the papers published in this issue.

Additive manufacturing (AM) technologies have gained considerable attention in recent years as an innovative method to produce high entropy alloy (HEA) components. The unique and excellent mechanical and environmental properties of HEAs can be used in various demanding applications, such as the aerospace and automotive industries. This review paper aims to inspect the status and prospects of research and development related to the production of HEAs by AM technologies. Several AM processes can be used to fabricate HEA components, mainly powder bed fusion (PBF), direct energy deposition (DED), material extrusion (ME), and binder jetting (BJ). PBF technologies, such as selective laser melting (SLM) and electron beam melting (EBM), have been widely used to produce HEA components with good dimensional accuracy and surface finish. DED techniques, such as blown powder deposition (BPD) and wire arc AM (WAAM), that have high deposition rates can be used to produce large, custom-made parts with relatively reduced surface finish quality. BJ and ME techniques can be used to produce green bodies that require subsequent sintering to obtain adequate density. The use of AM to produce HEA components provides the ability to make complex shapes and create composite materials with reinforced particles. However, the microstructure and mechanical properties of AM-produced HEAs can be significantly affected by the processing parameters and post-processing heat treatment, but overall, AM technology appears to be a promising approach for producing advanced HEA components with unique properties. This paper reviews the various technologies and associated aspects of AM for HEAs. The concluding remarks highlight the critical effect of the printing parameters in relation to the complex synthesis mechanism of HEA elements that is required to obtain adequate properties. In addition, the importance of using feedstock material in the form of mix elemental powder or wires rather than pre-alloyed substance is also emphasized in order that HEA components can be produced by AM processes at an affordable cost.

Metal additive manufacturing (AM) technologies are classified into two groups according to the consolidation mechanisms and densification degrees of the as-built parts. Densified parts are obtained via a single-step process such as powder bed fusion, directed energy deposition, and sheet lamination AM technologies. Conversely, green bodies are consolidated with the aid of binder phases in multi-step processes such as binder jetting and material extrusion AM. Green-body part shapes are sustained by binder phases, which are removed for the debinding process. Chemical and/or thermal debinding processes are usually devised to enhance debinding kinetics. The pathways to final densification of the green parts are sintering and/or molten metal infiltration. With respect to innovation types, the multistep metal AM process allows conventional powder metallurgy manufacturing to be innovated continuously. Eliminating cost/time-consuming molds, enlarged 3D design freedom, and wide material selectivity create opportunities for the industrial adoption of multi-step AM technologies. In addition, knowledge of powders and powder metallurgy fuel advances of multi-step AM technologies. In the present study, multi-step AM technologies are briefly introduced from the viewpoint of the entire manufacturing lifecycle.

Metal Powder Production for Additive Manufacturing

The findings presented in this paper stem from the survey of unclassified literature on additive manufacturing (AM)/3D printing technologies and their metrology (science of measurements). AM technologies allow engineers to design and build parts more freely than ever before. They also help to make production more distributed and eliminate obsolescence. This paper introduces different types of AM, as well as metrology challenges that NSWC Corona, the leading agency for the US Navy's Metrology and Calibration (METCAL) program, needs to address. It discusses potential uses, process limitations and metrology related to three popular categories of AM technologies; material extrusion (e.g., fused deposition modelling), powder bed fusion (e.g., selective laser melting) and directed energy deposition (e.g., laser-engineered net shaping). Powder bed fusion and directed energy deposition have proved capable of firearm and aerospace-grade manufacturing. AM technologies demonstrate huge promise and may revolutionise design, manufacturing, logistics, maintenance and acquisition in the Navy. However, there are still multiple hurdles to overcome before AM becomes an effective component in the military toolset. As AM continues to advance, the only way to ensure these new technologies fit as reliable pieces of the warfighter arsenal is to prioritise the development of corresponding measurement techniques and calibration schedules.

Additive Manufacturing (AM) technologies, which were developed around 30 years ago, are still evolving. They are applied in different sectors such as aeronautics, automotive, health, etc. There are different AM technologies: binder jetting, direct energy deposition, material extrusion, material jetting, powder bed fusion, sheet lamination and vat photopolimerisation. Amongst all of them, material extrusion is the most common technique used nowadays, due to several reasons: manufacture of parts is easy and cost-effective, desktop 3D printers are affordable, and they allow the use of many different materials. Within this AM category, two main techniques can be highlighted: FFF (Fused Filament Fabrication), also known as FDM (Fused Deposition Modelling), and DIW (Direct Ink Writing). FFF is the most typical technology which can offer multimaterial 3D printed parts. In addition, it can be mixed with other AM technologies in order to build hybrid 3D printers. Main applications of the FFF technology in the medical sector, which are explained in detail in the present chapter, are the manufacture of training models and surgical planning prototypes, medical devices, surgical guides, bio-active scaffolds, and cell 3D-bioprinting, etc. During the global pandemic of COVID-19, the FDM technology allowed to print different devices such as face masks or artificial breathers, among others.

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.

Influence of resin infiltrants on mechanical and thermal performance in plaster binder jetting additive manufacturing

Manufacturing processes are typically divided into three categories: formative, subtractive, and additive. While formative and subtractive manufacturing processes are considered more traditional, additive manufacturing (AM) is a family of evolving technologies that are rapidly growing with techniques and constraints yet to be explored. In this paper, a life cycle assessment comparison of casting (formative), machining (subtractive), and three AM methods, namely, binder jetting (BJ), powder bed fusion (PBF), and novel bound powder extrusion (BPE) has been performed. To compare each method from the sustainability standpoint, a life cycle assessment was conducted on a double cardan H-yoke, as a case study, focusing on environmental metrics such as water consumption, energy requirements, and CO2 emissions. This study focuses on the environmental effects of the novel BPE process with respect to current traditional manufacturing and AM methods. The case study was divided into two scenarios of the original and topology-optimized H-yoke to investigate the potential environmental footprint reduction by utilizing the capability of AM in generating complex geometries. The results proved that casting, as a formative manufacturing process, is the most environmentally friendly option for large-scale production of the investigated processes. Among the AM technologies that have been studied, PBF was the most environmentally friendly choice when coupled with renewable energy, reducing the total CO2 emission by 9.2% when compared to casting. In contrast, BJ was more environmentally friendly when fossil fuel was assumed as the main source of energy, showing only an 8.7% increase in CO2 emissions. The novel BPE preformed equal to or just short of BJ in all metrics, showing only a 9.4% increase of CO2 emission using fossil fuel compared to the 41.7% increase seen by PBF, with respect to BJ. AM environmental metrics were significantly improved when the topology-optimized part was employed. Machining, as a subtractive method, performed the worst from the environmental perspective due to the initial billet size and the amount of material to be removed (wasted). The production time for each process was analyzed to display the feasibility of producing the cast study part in a mass manufacturing scenario. The LCA case study proves that the increased number of BPE manufacturing steps does not negatively affect the environmental impact of the process, based on current LCA data. However, the BPE process is the most time-consuming process and must be considered when selecting the method of manufacture.

Inconel 718 is a nickel-based superalloy known for its excellent combination of high-temperature strength, corrosion resistance, and weldability. Additive Manufacturing (AM) has revolutionized traditional manufacturing processes by enabling the creation of complex and customized components. In this work, three prominent AM techniques: Laser-Based Powder Bed Fusion (PBF), Wire Direct Energy Deposition (DED), and Binder Jet (BJ) processes were explored. A thorough metallographic analysis and comparison of samples was conducted after short-term creep testing originating from each of the three aforementioned techniques in addition to wrought material. Detailed electron microscopy unveiled equiaxed grains in both BJ and wrought samples while PBF samples displayed elongated finer grain structures in the build direction, characteristic of PBF. The DED samples revealed a more bimodal grain distribution with a combination of smaller equiaxed grains accompanied by larger more elongated grains. When assessing the three processes, the average grain size was found to be larger in the BJ samples, while the PBF samples exhibited the most significant variation in grain and sub-grain size. Number density, size, and shape of porosity varied between all three techniques. Post-creep test observations in PBF samples revealed the occurrence of wedge cracking at the failure point, accompanied by a preference for grain boundary creep void formation while BJ samples exhibited grain boundary creep void coalescence and cracking at the failure location. In the DED samples, void formation was minimal however, it seemed to be more prevalent in areas with precipitates. In contrast, the wrought sample showed void formation at the failure site with a preference for areas with primary carbide formation. Despite BJ samples demonstrating similar or even superior rupture life compared to other AM techniques, a noteworthy reduction in rupture ductility was observed. While a coarse, uniform grain size is generally linked to enhanced creep resistance and rupture life, the combination of pre-existing voids along grain boundaries and the formation of new voids is hypothesized to accelerate rapid fracture, resulting in diminished ductility. This research shows careful consideration is needed when selecting an AM technology for high- temperature applications as creep behavior is sensitive to the large microstructural variations AM can introduce.

Many additive manufacturing (AM) technologies rely on powder feedstock, which is fused to form the final part either by melting or by chemical binding with subsequent sintering. In both cases, process stability and resulting part quality depend on dynamic interactions between powder particles and a fluid phase, i.e., molten metal or liquid binder. The present work proposes a versatile computational modeling framework for simulating such coupled microfluid-powder dynamics problems involving thermo-capillary flow and reversible phase transitions. In particular, a liquid and a gas phase are interacting with a solid phase that consists of a substrate and mobile powder particles while simultaneously considering temperature-dependent surface tension and wetting effects. In case of laser–metal interactions, the effect of rapid evaporation is incorporated through additional mechanical and thermal interface fluxes. All phase domains are spatially discretized using smoothed particle hydrodynamics. The method’s Lagrangian nature is beneficial in the context of dynamically changing interface topologies due to phase transitions and coupled microfluid-powder dynamics. Special care is taken in the formulation of phase transitions, which is crucial for the robustness of the computational scheme. While the underlying model equations are of a very general nature, the proposed framework is especially suitable for the mesoscale modeling of various AM processes. To this end, the generality and robustness of the computational modeling framework is demonstrated by several application-motivated examples representing the specific AM processes binder jetting, material jetting, directed energy deposition, and powder bed fusion. Among others, it is shown how the dynamic impact of droplets in binder jetting or the evaporation-induced recoil pressure in powder bed fusion leads to powder motion, distortion of the powder packing structure, and powder particle ejection.

Aiming for innovative ceramic manufacturing technologies which enable creative and novel products, a national R&D project “High-Value Added Ceramic Products Manufacturing Technologies (HCMT)” has been initiated since 2014 as part of the Council for Science, Technology and Innovation (CSTI), Cross-ministerial Strategic Innovation Promotion Program (SIP), “Innovative design/manufacturing technologies” program in Japan. The project deals with two key technologies: additive manufacturing (AM) for realizing complex-shaped ceramic products and reducing their lead-times, and hybrid coating on 3D bodies for enhancing their functionality and durability. Following an overview of this project and a brief description on the general status of AM technologies, this article focuses on the R&D strategies and the latest achievements on AM of ceramics in this project. Among a variety of AM approaches, we employ two AM technologies for making ceramic green bodies; powder layer manufacturing (powder bed fusion or indirect selective laser sintering) and slurry layer manufacturing (vat photo-polymerization or stereolithography), because of their dimensional accuracy, shape-flexibility, density-adjustability, etc. The former is a dry forming process, and is suitable for large/porous components, while the latter is a wet one, being good for small/dense parts. In addition, intensive research efforts are being devoted to ceramic laser sintering (direct selective laser sintering) which enables concurrent forming and sintering (saving post-sintering-process). This paper describes several 3D prototype models produced for various application targets using the developed AM technologies, which are never attainable with conventional methods. The current issues and future perspective for AM of ceramics will be addressed and discussed as well.

Chapter 2 - Additive manufacturing technology

Additive manufacturing (AM) of hot-work tool steels such as H13 offers unique opportunities for producing complex, conformally cooled tools with reduced production time and material waste. In this study, five metal AM technologies—Fused Deposition Modeling and Sintering (FDMS, Desktop Metal Studio System and Zetamix), Binder Jetting (BJ), Laser Powder Bed Fusion (LPBF), and Directed Energy Deposition (DED)—were compared in terms of microstructure, porosity, and post-processing heat treatment response. The as-printed microstructures revealed distinct differences among the technologies: FDMS and BJ exhibited high porosity (6–9%), whereas LPBF and DED achieved near-full densification (<0.1%). Samples with sufficiently low porosity (BJ, LPBF, DED) were subjected to tempering and quenching treatments to evaluate hardness evolution and microstructural transformations. The satisfactory post-treatment hardness was observed in both tempered and quenched and tempered BJ samples, associated with secondary carbide precipitation, while LPBF and DED samples retained stable martensitic structures with hardness around 600 HV0.5. Microstructural analyses confirmed the dependence of phase morphology and carbide distribution on the thermal history intrinsic to each AM process. The study demonstrates that while FDMS and BJ are more accessible and cost-effective for low-density prototypes, LPBF and DED offer superior density and mechanical integrity suitable for functional tooling applications.