Ceramic Parts Research Articles

Development of a Polyethylene Glycol/Polymethyl Methacrylate-Based Binder System for a Borosilicate Glass Filler Suitable for Injection Molding.

Powder injection molding is an established, cost effective and often near-net-shape mass production process for metal or ceramic parts with complex geometries. This paper deals with the extension of the powder injection molding process chain towards the usage of a commercially available borosilicate glass and the realization of glass compounds with huge densities. The whole process chain consists of the individual steps of compounding, molding, debinding, and sintering. The first part, namely, the search for a suitable feedstock composition with a very high solid load and reliable molding properties, is mandatory for the successful manufacture of a dense glass part. The most prominent feature is the binder composition and the related comprehensive rheological characterization. In this work, a binder system consisting of polyethylene glycol and polymethylmethacrylate with stearic acid as a surfactant was selected and its suitability for glass injection molding was evaluated. The influence of all feedstock components on processing and of the process steps on the final sintered part was investigated for sintered glass parts with densities around 99% of the theoretical value.

Particle surface oxidation modification and particle gradation strategy for the preparation of high-strength SiC ceramics via vat photopolymerization

The high refractive index, high absorbance, and low sintering activity of SiC powders pose challenges in achieving sufficient curing depth of SiC slurries and achieving densification of SiC ceramics. Hence, the preparation of high-strength SiC ceramics by vat photopolymerization is a challenge. This study proposes a strategy of particle surface oxidation modification and particle gradation to address this difficulty. Specifically, the surface of micron and submicron SiC particles is oxidatively modified to enhance the curing depth of SiC slurry, and the gradation of these particles is optimized to improve the sintering activity of the SiC particle system. The percentage of oxidized micron and submicron SiC particles is carefully adjusted to meet the requirements of both vat photopolymerization preparation and sintering. It found that increasing the percentage of sub-micron particles in the particle grade system had a negative impact on the rheological and curing properties of the slurry but contributed to the stability of the slurry and the performance of the sintered ceramic parts. Ensuring that the percentage of sub-micron particles reaches 50% or higher and reducing direct contact between micron particles to form sintered necks are two key conditions for the preparation of high-strength SiC ceramics. Additionally, it found that interlayer bonding location is the pore defects concentrated in the sintered ceramic parts, providing direction for further optimization of ceramic properties. By implementing the oxidation modification and particle gradation optimization strategy, the densification and three-point flexural strength of SiC ceramic parts were improved significantly. The relative density and three-point flexural strength of SiC increased from 65.7 ± 5.3% to 86.8 ± 3.7% and from 75.0 ± 2.1–170.9 ± 11.6 MPa, respectively. This approach provides a simple and effective method to prepare high-strength SiC ceramics by vat photopolymerization.

Uniform rate debinding for Si3N4 vat photopolymerization 3D printing green parts using a specific-stage stepwise heating process

Vat photopolymerization is regarded as one of the most promising 3D printing technologies to process ceramics. However, achieving crack-free debinding in ceramic green parts, particularly with larger volumes or cross-sectional areas, presents a great challenge and often represents the most time-consuming stage. Here we develop a specific-stage stepwise heating process based on the multi-component resin system decomposition and the weight loss characteristics to achieve the decomposition of resin with a uniform rate, thereby avoiding cracks due to the severe gas expansion and the increase of dramatic internal stress. A formula about the uniform rate decomposition of resin is established, enabling precise predictions regarding the residual resin weight at different stages during the debinding process. The validity of the specific-stage stepwise heating process is verified through the examination of Si3N4 vat photopolymerization 3D printing green parts, known for being challenging to debinding compared to other ceramic fillers. The crack-free debinding of Si3N4 printed green parts increases in sizes corresponding to the increasing T-value of the specific-stage stepwise heating process. This enables the selection of an appropriate T-value based on the printed green part's wall thickness, thereby enhancing debinding efficiency. Notably, setting the T-value to 1200 min can successfully debinding an 11 mm wall-thickness cube green parts without cracking. The specific-stage stepwise heating process is expected to be versatile across various resin and ceramic systems and plays a crucial role in the comprehensive exploitation of the design freedom offered by ceramic vat photopolymerization 3D printing.

Four-dimensional printing of polymer-derived ceramics with high-resolution, reconfigurability, and shape memory effects

Owing to their high thermal stability, oxidation resistance, and corrosion resistance, polymer-derived ceramics (PDCs) have attracted extensive attentions to fabricate complex-shaped ceramic parts that can be used in high-tech industries. While flexible PDCs offer structural reconfiguration, methods for inducing shape changes primarily rely on mechanical loads, such as manual loading, motors, or pneumatic pumps, which is considered impractical and requires complex control systems. To address these issues, a vat photopolymerization (VPP)-based four-dimensional (4D) printing method has been proposed and developed to manufacture PDCs with reconfigurable and shape memory effects for the first time. This innovative 4D printing method is highly programmable and compatible with VPP technology, allowing the fabrication of high-resolution, intricately designed ceramic structures with a high solid content. Through a two-step curing process, autonomous shape transformations of the PDCs have been achieved.

High‐strength Si–SiC lattices prepared by powder bed fusion, infiltration‐pyrolysis, and reactive silicon infiltration

AbstractThis study focuses on the design, additive manufacturing, and characterization of silicon carbide‐based components with complex geometries. These parts were produced using a novel hybrid technique, previously developed: powder bed fusion of polyamide was used to 3D print two different templates with complex architectures. Preceramic polymer infiltrations and pyrolysis with polycarbosilane and furan resin were performed to obtain the ceramic parts. The final densification was achieved with reactive or nonreactive silicon infiltrations according to four different strategies, producing ceramics comprised of crystalline βSiC, reaction‐bonded βSiC, and low residual silicon. The final gyroid samples (∼70 vol% macroporosity) exhibited a maximum compressive strength of 24.7 ± 2.2 MPa, with a skeleton density of 3.173 ± 0.022 g/cm3, and a relative density of 0.935 ± 0.016. These findings underscore the potential of this manufacturing approach and showcase its effectiveness in fabricating intricate ceramic structures for engineering applications as heat exchangers and catalytic supports.

Rapid geometric characterization of ceramics fragments through split Hopkinson pressure bar tests

AbstractThe research on fracture mechanisms of brittle materials is extremely difficult such as the determination of the energy absorption modes and the geometric characteristics of debris. In this paper, a dynamic experimental fragment recovery device was developed to study the facture characteristics of A99 ceramics (the mass of Al2O3 accounts for 99%) based on the Split‐Hopkinson pressure bar (SHPB) experiments, in which the energy absorption mechanism was revealed. A three‐view characterization method was developed to obtain the geometric characterization formula under various strain rate; therefore, the geometric parameters of the fragments can be quickly characterized. The failure mode was investigated in correlation between strain rate and micro‐cracks. It was found that the shape of the strain rate controlled the proportion of dissipated energy. At a lower strain rate the fragment was prone to needle shape, while at a higher strain rate (above 2001 s−1) the proportion of dissipated energy increased to 72% and the fragment shape tended to be nearly spherical. A formula based on strain rate was proposed to characterize the geometric parameters of the fragments without the need of geometry dimensions; therefore, the fragment rate can be quickly obtained, which could provide guidance for the design of ceramics parts.

Direct 4D printing of ceramics driven by hydrogel dehydration

4D printing technology combines 3D printing and stimulus-responsive materials, enabling construction of complex 3D objects efficiently. However, unlike smart soft materials, 4D printing of ceramics is a great challenge due to the extremely weak deformability of ceramics. Here, we report a feasible and efficient manufacturing and design approach to realize direct 4D printing of ceramics. Photocurable ceramic elastomer slurry and hydrogel precursor are developed for the fabrication of hydrogel-ceramic laminates via multimaterial digital light processing 3D printing. Flat patterned laminates evolve into complex 3D structures driven by hydrogel dehydration, and then turn into pure ceramics after sintering. Considering the dehydration-induced deformation and sintering-induced shape retraction, we develop a theoretical model to calculate the curvatures of bent laminate and sintered ceramic part. Then, we build a design flow for direct 4D printing of various complex ceramic objects. This approach opens a new avenue for the development of ceramic 4D printing technology.

A real-time detection system for multiscale surface defects of 3D printed ceramic parts based on deep learning

3D printed ceramic parts often have defects due to their inherent brittleness. These defects are of various scale sizes. Detecting these defects, especially with multiple sizes, is a challenging task in the field of detection. Furthermore, there is a lack of surface defect real-time detection systems suitable for industrial applications in this field. Based on this, this paper makes two contributions: the design and development of a real-time defect detection system, and the proposal of a multiscale defect detection method for 3D printed ceramic surfaces within this system. Firstly, the paper establishes the overall structure of the real-time detection system for surface defects on 3D printed ceramic components, and describes the hardware and software components of the system. On this basis, a dataset of ceramic surface defect images is collected and constructed. Then, experimental analyses point out the shortcomings of the You Only Look Once version-5 (YOLOv5) model for multiscale defect detection. To address the shortcomings, the YOLOv5 model is optimized from three aspects, resulting in the Deep separable convolution + residual network-SKNetwork-Efficient Channel Attention Network-YOLOv5 (DepRes-SK-ECA-YOLOv5) model for multiscale defect detection. This model improves the ability to extract and fuse features of defects at different scales. The experimental results show that the DepRes-SK-ECA-YOLOv5 model can achieve 93.5 %, 91.6 %, 94.3 %, and 0.198 s for Precision, Recall, mAP, and Speed for the test set, respectively. Finally, the paper designs the workflow for the system software. The system hardware and system software are integrated to form a real-time detection system. The performance of the detection system is verified through experiments.

Micromilling of high-aspect-ratio ceramic thin walls with customized micro PCD end mills

With the increasing application of ceramic structural parts, how to realize the ductile cutting of ceramics and high-quality machining of ceramic structural parts have become an important research direction. In this paper, the micromilling of fully sintered zirconia ceramics is studied using customized PCD end mills with three different rake angles. The critical thickness for microcutting of ceramics during the micromilling process is theoretically analyzed and experimentally identified. Then, the ductile cutting of ceramic materials is to be realized by controlling the key cutting parameter (feed per tooth fz) considering the critical cutting thickness. Under the condition of ductile cutting, the high-aspect-ratio vortex curved thin walls of fully sintered zirconia ceramics are successfully fabricated. Furthermore, the tool wear of the customized PCD end mill is analyzed. The tool geometric parameters that are beneficial to ensure both ductile cutting and high tool life are identified.

Exploring the Mpemba effect: a universal ice pressing enables porous ceramics.

Piezoceramics with global porosity and local compaction are highly desired to exploit the combination of mechanical and electrical properties. However, achieving such a functional combination is challenging because of the lack of techniques for applying uniform pressure inside porous ceramic green parts. Nature provides many examples of generating strong forces inside the macro and micro channels via the state transformation of water. Inspired by these phenomena, we present a technique of "ice and fire", that is, water freezing (ice pressing) and high-temperature sintering (fire), to produce ideal porous piezoceramics. We introduce a new compaction method called the "ice pressing method", which manipulates liquid phase transition for compaction. This method has several advantages, including uniform pressure distribution, a wide pressure range, high effectiveness, and selective freezing. It can generate an ultrahigh pressure of up to 180 MPa on the piezoceramic green skeletons in minutes while retaining their functional pore structures. By exploiting the Mpemba phenomenon, we further accelerate the compaction procedure by 11%. The first ice-pressed and second fire-consolidated lead zirconate titanate (PZT) ceramics are highly densified and exhibit an outstanding piezoelectric response (d33 = 531 pC N-1), comparable to conventional pressed bulk counterparts and 10-20 times higher than those of unpressed materials. The novel ice pressing method breaks the limitation of lacking a compaction technique for porous ceramics. The versatile and effective ice pressing method is a green and low-cost route promoting applications in sensors, acoustics, water filtration, catalyst substrates, and energy harvesting.

Results of experimental simulation of interaction between corium of a nuclear reactor and sacrificial material (Al<sub>2</sub>O<sub>3</sub>) with a lead layer

<abstract> <p>This paper presents the results of an experimental study of the interaction of a candidate sacrificial material (SM) for a light water reactor melt trap with corium at the Lava-B test-bench. The candidate sacrificial material is a combination of aluminum oxide and a lead layer. The idea of using such a combination of SM is based on the fact that when the lead layer interacts with corium, there will be an increase in the intensity of heat removal from the corium, as well as the chemical interaction between the corium and SM due to the high heat-conducting properties of lead. This approach will improve the efficiency of corium localization in the melt trap compared to the current set of sacrificial material. Experiments have shown active melting and boiling of lead during its interaction with corium. This is confirmed both by the readings of thermocouples and by the X-ray diffraction phase analysis of the deposit material formed on the walls of the melt receiver (MR) of the Lava-B bench, sampled after the experiment. The experiment results show that the lead layer reduces the rate of increase in the temperature of the corium and increases the rate of erosion of the ceramic part of the SM. With these circumstances, it is possible to conclude that the use of aluminum oxide with a lead layer is promising in practice.</p> </abstract>

Comparison of Additively Manufactured Polymer-Ceramic Parts Obtained via Different Technologies.

This paper aims to compare two ceramic materials available for additive manufacturing (AM) processes-vat photopolymerization (VPP) and material extrusion (MEX)-that result in fully ceramic parts after proper heat treatment. The analysis points out the most significant differences between the structural and mechanical properties and the potential application of each AM technology. The research revealed different behaviors for the specimens obtained via the two mentioned technologies. In the case of MEX, the specimens exhibited similar microstructures before and after heat treatment. The sintering process did not affect the shape of the grains, only their size. For the VPP specimens, directly after the manufacturing process, irregular grain shapes were registered, but after the sintering process, the grains fused, forming a solid structure that made it impossible to outline individual grains and measure their size. The highest compression strength was 168 MPa for the MEX specimens and 81 MPa for the VPP specimens. While the VPP specimens had half the compression strength, the results for the VPP specimens were significantly more repeatable.

Elimination of delamination cracks in ceramics manufactured using LCD stereolithography

LCD stereolithography of ceramics allows the creation of ceramic parts with unprecedented resolution for various applications from medical tooling to archeological restoration. However, the manufacturing of a delamination cracks-free sintered part using LCD stereolithography has been an arduous challenge in both industrial and academic research. This contribution is a guide for the elimination of such delamination cracks. Photo-rheology, instrumented indentation tests, UV/Vis spectrophotometry and multiple microscopy techniques were used to analyze the formation of delamination cracks and to identify their culprits. It was found that proper particle dispersion, sufficient air extraction, optimized slurry formulation, optimized printing parameters and sound design principles jointly contribute to the manufacturing of a delamination cracks-free ceramic part using LCD stereolithography. This research addresses each of the aforementioned factors, with the goal of improving the quality of ceramic parts and increasing their functionality for various applications.

A single-sensor multi-scale quality monitoring methodology for laser-directed energy deposition: Example with height instability and porosity monitoring in additive manufacturing of ceramic thin-walled parts

Laser Additive Manufacturing (LAM) faces various technical challenges, encompassing issues with dimensional accuracy, mechanical properties, and processing-related defects, such as surface roughness, cracking, and residual porosity. Currently, the quality of safety-critical parts produced by LAM processes, which is still improved through trial-and-error adjustments of multiple process variables, have limited real-time monitoring capabilities. This study introduces an innovative method for real-time quality assessment of laser-directed energy deposition (LDED) procedures across multiple scales (macroscale, mesoscale, and microscale) utilizing a single sensor. This approach is founded on two fundamental components: the single-sensor system for data acquisition and the algorithm for simultaneous multi-scale quality monitoring. For the data acquisition system aspect, a single-sensor, high dynamic range (HDR), multi-scale information acquisition system has been developed to mitigate intense radiation, eliminate plume disturbances, and rectifies backlight shadows, facilitating clearer images of deposition contours and the molten pool region. In the realm of data monitoring algorithms, a physics model-driven supervisory algorithm is employed to enable monitoring of contour height instability, while a convolutional neural network (CNN), driven by image data, is utilized for porosity prediction. Then, this algorithm adeptly tackles the challenge of simultaneously monitoring macroscopic contour and mesoscale porosity. Regarding the validation of the method, the outcomes of single-sensor multi-scale quality monitoring in additive manufacturing of ceramic thin-wall parts indicate a 100% recognition rate for deposition contour and molten pools, contour feature recognition with a relative error of under 0.05%, porosity prediction accuracy surpassing 99%, and a monitoring time of 80.4 ms per frame. Single-sensor multi-scale real-time quality monitoring can serve as a methodological support for future real-time quality control in LDED.

Fused Filament Fabrication for Metallic Materials: A Brief Review.

Fused filament fabrication (FFF) is an extrusion-based additive manufacturing (AM) technology mostly used to produce thermoplastic parts. However, producing metallic or ceramic parts by FFF is also a sintered-based AM process. FFF for metallic parts can be divided into five steps: (1) raw material selection and feedstock mixture (including palletization), (2) filament production (extrusion), (3) production of AM components using the filament extrusion process, (4) debinding, and (5) sintering. These steps are interrelated, where the parameters interact with the others and have a key role in the integrity and quality of the final metallic parts. FFF can produce high-accuracy and complex metallic parts, potentially revolutionizing the manufacturing industry and taking AM components to a new level. In the FFF technology for metallic materials, material compatibility, production quality, and cost-effectiveness are the challenges to overcome to make it more competitive compared to other AM technologies, like the laser processes. This review provides a comprehensive overview of the recent developments in FFF for metallic materials, including the metals and binders used, the challenges faced, potential applications, and the impact of FFF on the manufacturing (prototyping and end parts), design freedom, customization, sustainability, supply chain, among others.

Effect of particle size distribution and printing parameters on alumina ceramics prepared by Additive Manufacturing

Vat photopolymerization-based additive manufacturing is a promising technology for the preparation of ceramic parts, owing to its short fabrication cycle and low manufacturing cost. However, its application is limited due to the low mechanical properties and deformation of ceramic parts. To improve the properties of ceramic parts, changing particle size and printing parameters have been found to be useful. Herein, alumina ceramic parts were prepared using three different powders with different particle size (Powder A: D50 = 1.3 μm, D90 = 6.1 μm; Powder B: D50 = 3.4 μm, D90 = 10.0 μm; Powder C: D50 = 1.3 μm, D90 = 2.8 μm), different layer thickness (50 μm, 75 μm, 100 μm), and different curing times (1 s, 3 s, 5 s, 8 s). The ceramics prepared with Powder A and Powder C, which possessed the same D50, had almost the same flexural strength, indicating that the flexural strength is closely related to the particle size and its distribution. With the increase in layer thickness, the flexural strength was increased. When the layer thickness was 100 μm, the flexural strength reached 18.5 MPa when samples were prepared with Powder A and Powder C. At the same time, the flexural strength firstly increased and subsequently decreased with increasing curing time. Based on the flexural strength and shrinkage of the sintered ceramics, using Powder A, layer thickness of 50 μm, and curing time of 5 s were regarded as the best fabrication conditions. The results indicate that adjusting powder particle size distribution, layer thickness, and curing time are promising methods for the fabrication of 3D printed ceramics with optimized properties.

Effect of laser power, speed and offset on the welding performance of 304 SS/Al2O3 ceramics

In this study, 304 SS/Al2O3 ceramic structural parts were successfully prepared by laser heat source biasing using AgCuTi as filler. The method removes residual thermal stresses by retaining unfused 304 SS (stainless steels), provides protection to the Al2O3 ceramics, and connects the two sides of the substrate using the wettability of the AgCuTi filler. Based on the 304 SS/Al2O3 connectivity, the Gibbs free energy changes of Ti–Fe and Ti–Cu compounds at the weld were calculated from the thermodynamics perspective to determine the possible phases. The temperature field of the joint was also investigated using finite element simulation to analyze the temperature changes in the fusion zone, the interface I (304 SS/AgCuTi), and the interface II (AgCuTi/Al2O3) under different welding parameters, and predict the welding parameters that can achieve an effective connection without destroying the Al2O3 ceramics, which were experimentally verified. The maximum tensile strength of the joints was 94.9 MPa when the laser power was increased from 372 W to 432 W. The maximum tensile strength of the joints was 90.5 MPa when the laser speed was increased from 440 mm/min to 630 mm/min. The maximum tensile strength of the joints was 89 MPa when the laser offset was increased from 1.4 mm to 1.9 mm. By analyzing the microstructure, it was found that brittle intermetallic compounds (IMCs) such as FeTi and Cu2Ti were generated at interface I, which was the main factor affecting the strength of the joint. Many Ag(s,s) and Cu(s,s) solid solutions were found at AgCuTi and interface II. By analyzing the microstructure, the interface organization of the joint is composed of 304 SS + α-Fe/γ-Fe + FeTi/Cu2Ti + Ag(s,s)/Cu(s,s) + Ti2Cu + Al2O3. Finally, the Arrhenius function calculates the diffusion coefficients and diffusion concentrations of Ti and Fe elements.

Shrinkage, microstructure, and mechanical properties of sintered 3D‐printed silica via stereolithography

AbstractStereolithography has been used to create ceramic parts with complex geometry that is difficult to achieve with conventional fabrication techniques. This study used stereolithography to print silica honeycomb structures with a commercial Formlabs Form2 printer. The printed samples were sintered at different temperatures, and the print shape was retained up to 1300°C, but significant distortion from partial melting occurred at 1400°C. Higher sintering temperatures lead to more shrinkage, but it is non‐uniform among directions, with the open cell plane shrinking more than the dense plane of the sample. As expected, the density of samples also increases with the sintering temperature. At higher sintering temperatures, there is an increase in cristobalite and a decrease in quartz, tridymite, and amorphous silica. Regarding mechanical properties, the out‐of‐plane compressive strength is approximately one order of magnitude higher than the in‐plane compressive strength. When compressed along the out‐of‐plane direction, the samples sintered at lower temperatures surprisingly exhibit higher strength, which is explained by the micro‐cracking mechanism. As expected, the samples sintered at higher temperatures display higher strength when compressed along the in‐plane direction.

A thermal-initiated monomer binder enhancing green strength with low binder saturation for binder jetting additive manufacturing of cemented carbide

Binder jetting (BJ) additive manufacturing (AM) technology is a competitive technology for fabricating ceramic and metal parts. In most cases, a high level of binder saturation is necessary to achieve sufficient strength for the green part. However, the oversaturated binder may lead to shape distortion and excess carbon residual of the green part. To solve the problem, a novel binder consisting of HEMA (2-Hydroxyethyl methacrylate) monomer and HDDA (1,6-Hexanediol diacrylate) monomer was proposed to improve the green strength and reduce carbon residual of parts at a low level of binder saturation. The monomer binder curing under the thermal-initiated free radical induced polymerization. This paper studies the printability, pyrolysis, and curing kinetics of the monomer binder, and investigates the effect of binder saturation on the strength and dimensional accuracy of WC-12Co green parts. The experimental results show that the monomer binder enables WC-12Co green parts to achieve a transverse rupture strength (TRS) of 0.66 MPa at a low binder saturation of 20%, and exhibits high dimensional accuracy. Additionally, the binder exhibited a high pyrolysis efficiency of 97.66%, resulting in a low residual carbon content of less than 0.3 wt% after debinding. This favorable pyrolysis characteristic does not compromise the phase composition of the WC-12Co matrix during the sintering process. This paper provides a new solution for fabricating cemented carbide parts with BJ AM technology.

Preparation and characteristics of honeycomb mullite ceramics with controllable structure by stereolithography 3D printing and in-situ synthesis

Porous honeycomb mullite ceramics were controllably fabricated in-situ using stereolithography 3D printing. The effects of the dispersant type and content on the rheological behavior of the mullite precursor slurry were investigated. Additionally, the influence of the debinding atmosphere (air and argon) on the quality of the samples and formation of cracks was also studied. The results indicated that oleic acid (OA), 3-glycidoxypropylthrimethoxysilane (KH560), and disperbyk (BYK111) displayed the capability to create low-viscosity and highly stable slurries. Among these KH560 was proved to be the most effective. The mullite precursor slurry containing 4 wt% KH560 dispersants exhibited a shear thinning behavior. It displayed a viscosity of 0.26 Pa·s at a shear rate of 30 s−1. The mullite ceramic parts displayed good a dimensional resolution at an exposure dose of 5.47 mJ/cm2. During the debinding process, the printed parts were susceptible to cracking and deformation in air, but remained devoid of defects in argon. When the samples were sintered at 1600 °C, the corundum phase transformed almost completely into the mullite phase. The linear shrinkage values were 5.81%, 6.33%, and 10.26% in the O-X, O–Y and O-Z directions, respectively.