Relationship between topological structures and mechanical properties of artificially architected SiC cellular ceramics: Experimental and numerical study

Due to their topological superiority, the architected materials facilitate the improvement of the physical and mechanical properties of cellular materials. With the progress of additive manufacturing technologies, the fabrication of architected silicon carbide (SiC) cellular ceramics has become achievable. This study focuses on the indirect additive manufacturing method of SiC cellular ceramics consisting of 3D printing, replication, and reaction-bonded sintering. To study the impact of the topology on the mechanical performance, three strut-based unit cell structures and stochastic foam with robust solid struts were experimentally and numerically studied. Results showed that the hexahedron structure has the highest compression strength, the tetrakaidecahedron structure has the highest flexural strength, while the regular structures have higher mechanical performance than the stochastic foam. The deformation mechanisms of the topologies under the compression load indicated that the hexahedron, tetrakaidecahedron, and stochastic foam favor the bending-dominated deformation mode, while the octet favors the stretching-dominated deformation mode.     

Preparation and mechanical performance of SiCw/geopolymer composites through direct ink writing

Traditional geopolymer structures benefit from the durability, irradiation resistance, and environmental friendliness, but their brittleness limits their applications where repeated, impactive strains are imparted. This situation may be alleviated if complex structures with tunable geometry can be fabricated, for example, through 3D printing based on direct ink writing (DIW). In this research, SiC whisker/geopolymer (SiC_w/GP) composites were fabricated by the DIW for the first time. The rheological behaviors of the SiC_w/GP inks and the fracture behaviors of the printed samples were explored. The modified printing inks exhibited non-Newtonian fluid behavior (shear-thinning). Subsequently, a series of lightweight architected structures were fabricated, and they revealed how reinforcement and architecture of the printed structures could influence both the strength and toughness of the SiC_w/GP composites.     

磁场作用下冷冻铸造法制备仿生材料研究进展

随着科技的迅速发展,对材料的性能提出了更高的要求,迫切需要开发新型轻质高性能结构材料,即低密度、高刚度、高强度和高韧性等特点集于一身。生物材料经过数亿年的进化,形成了与环境和功能需求相适应的精细复杂结构,如贝壳珍珠层的“砖-泥”结构和螃蟹角质层的螺旋结构,它们均表现出非凡的机械性能和独特的功能特性,这启发了人们对于高性能材料的设计和构筑。目前发展的冷冻铸造法(即冰模板法)是制备仿生材料的一种有效方法,通常在温度梯度作用下定向凝固水基陶瓷浆料,经冷冻干燥后可获得具有精细结构的多孔陶瓷材料,随后对该多孔陶瓷填充软相-树脂后可获得仿珍珠贝结构陶瓷-树脂复合材料。为了进一步控制材料微观结构,研究人员对冷冻铸造过程施加磁场作用,最终发现材料的结构和性能均发生了明显变化。本文介绍了冷冻铸造法在控制材料微观结构以及制备仿生材料方面取得的一些进展,综述了施加磁场作用对冷冻铸造的影响,总结了施加磁场辅助的冰模板材料微观结构和机械性能变化规律。     

Effect of internal lattice structure on the flexural strength of 3D printed hierarchical porous ultra-high temperature ceramic (ZrB2)

3D printing of technical ceramics using direct ink writing (DIW) of multiphase colloidal inks has the unique ability to create structures with hierarchical features. To facilitate the application of 3D printed hierarchical porous ultra-high temperature ceramics (UHTCs), additional limiting factors such as strength and the effect of 3D printed internal lattice structure need to be better understood. This study reports on the strength dependence of common DIW print parameters including internal lattice structure shape, nozzle diameter and spacings between adjacent filaments. The present study applies Weibull statistics to the experimental array that considers macro features introduced through print parameters as flaw types, which shows strength of 3D printed hierarchical ZrB₂ is highly dependent on the introduced 3D printed structure, size and the stressed volume. This work provides essential information that can be used in the initial stages of design when considering implementation of additively manufactured hierarchical porous UHTCs.     

3D printing of open-porous cellular ceramics with high specific strength

We present a novel processing route for manufacturing highly open porous, hierarchically structured ceramics via direct ink writing. We manufactured cellular samples with overall porosities up to 88% that exhibit fully open-porous struts with porosities between 45 and 60% and pore sizes x_50,3 < 6 μm using capillary suspension based inks. An innovative processing strategy enabled manufacturing crack-free, undeformed cellular ceramic samples.We printed hexagonal honeycomb structures that showed exceptionally high specific strength under compression load and significantly enlarged the strength-density range that was covered by sintered capillary suspensions, so far. Without loss of mechanical strength the density of ceramic parts was decreased by about a factor of 2–3. Strength of in-plane and out-of-plane loaded hexagonal honeycomb structures varies according to common scaling laws for cellular structures. The honeycombs are mechanically more efficient than bulk specimens from capillary suspensions, since they show a distinctly lower sensitivity of strength on density.     

Bioceramics and their application for dental restoration

Abstract

This review article covers the historical development of ceramics, from the beginnings to the present. Feldspar based ceramic biomaterials for veneering metal frameworks, which are based on the jacket porcelain crown, have firmly established themselves in restorative dentistry since the 1970s. Currently, the development of restorative dental materials that can be used to replace metal represents a major challenge. As a result, this review will focus on the latest materials in this field. These materials include glass ceramics as well as high performance sintered ceramics. Glass ceramics exhibit more favourable optical properties, such as translucency and colour, compared with high performance ceramics, while the latter demonstrate high flexural strength and toughness. Both groups of materials have specialised applications in restorative dentistry and are capable of covering all the indications of dental restorations. The two types of materials, that is, glass ceramics and ceramics, have to be processed in accordance with their properties. As a result, the processing techniques, such as moulding, sintering and machining, will be discussed in detail in addition to the properties of the materials. Additional development possibilities for the materials will be presented on the basis of customer/patient needs and the successful long term use of glass ceramics and ceramics. In this context, it is clear that high performance ceramics and layered composites (consisting of high performance ceramics veneered with glass ceramics) offer the best possible solution for indications in the posterior region of the mouth. In contrast, glass ceramics are used to fabricate inlays and onlays for all parts of the jaw. In addition, glass ceramics can be used to fabricate crowns and small bridges to replace anterior dentition.     

High thermal-conductivity rGO/ZrB2-SiC ceramics consolidated from ZrB2-SiC particles decorated GO hybrid foam with enhanced thermal shock resistance

Graphene derivative materials exhibit excellent mechanical and thermal properties, which have been extensively used to toughen ceramics and improve thermal shock resistance. To overcome the thermal agglomeration of graphene oxide (GO) during heating and drying process, ZrB₂-SiC particles decorated GO hybrid foam with uniformly anchored ceramic particles was synthesized by electrostatic self-assembly and liquid nitrogen-assisted freeze-drying process. Densified rGO/ZrB₂-SiC ceramics with varying microstructure, thermal physical and mechanical properties were obtained by adjusting the content of decorated ceramic particles. Although the flexural strength of rGO/ZrB₂-SiC ceramics have an attenuation compared with that of ZrB₂-SiC ceramic, the thermal conductivity, work of fracture and thermal shock resistance are greatly improved. rGO/ZrB₂-SiC ceramics exhibit delayed fracture and increasing R-curve behavior during the crack propagation. The novel preparation technology allows for the well dispersion of rGO in ZrB₂-SiC ceramics and can be easily extended to other ceramic or metal materials systems.     

Stress–Strain Behavior of Alumina, Magnesia-Partially-Stabilized Zirconia, and Duplex Ceramics and Its Relevance for Flaw Resistance, KR-Curve Behavior, and Thermal Shock Behavior

The stress–strain behavior for Al₂O₃ of different grain size, for three different Mg-PSZ grades, and for various differently composed duplex structures is investigated and compared with their flaw resistance, K^R -curve behavior, and thermal shock behavior measured in previous works. The experimental results seem to reveal that, for most materials, quasi ductility increases with increasing flaw resistance, increasingly pronounced K^R -curve behavior, and increasing thermal shock retained strength. However, brittle ceramics can exhibit rising K^R -curves, whereas pronounced quasiductile materials can exhibit flat K^R -curves. An explanation for the apparent pseudo relationship between quasi ductility and K^R -curve behavior may be that, apart from genuine transformation ductility, most quasi-ductile effects such as microcracking have only a minor contribution to rising R -curve behavior, but require the existence of strong residual stresses, which are, on the other hand, responsible for the occurrence of most toughening mechanisms. Also discussed is the influence of microcracking on flaw resistance and thermal shock strength degradation.     

Preliminary Model of Radiation Damage in Ceramics

A preliminary model of radiation damage in binary ceramic oxides has been developed. The model described here accounts in an approximate way for some of the major differences between metallic alloys and ceramics that are believed to be responsible for the fact that ceramic materials appear in some cases to behave differently than metallic alloys when exposed to displacive irradiation. The model considers the influence of the existence of a second lattice and the additional constraint of stoichiometric point defects absorption by dislocation loops on the concentrations of point defects that would be observed at steady state in an irradiated ceramic. These point defect concentrations are then used to compute various measures of the sensitivity of these materials to the type of microstructural evolution that is observed in irradiated metals. Initial results indicate that both the lattice and stoichiometry effects can help to mitigate radiation damage in ceramics. However, the effect is not necessarily large. In agreement with recent data, the results indicate that at least some ceramic oxides may exhibit a sensitivity to displacement damage that is similar to metals.     

Lightweight porous silica ceramics with ultra-low thermal conductivity and enhanced compressive strength

In recent years, the need for robust thermal protection for reusable spacecraft and vehicles has spurred strong demand for high-performance lightweight thermal insulation materials that exhibit high strength. Herein, we report silica porous ceramics prepared via the direct foaming technique with lightweight, ultra-low thermal conductivity and enhanced compressive strength. Silica particles (particle size: 500 nm and 2 μm) were used as the raw materials. The nano-sized silica particles were easily sintered, thereby improving the compressive strength of the ceramics, whereas the micro-sized silica particles maintained the pore structure integrity without deformation. The addition of nano-silica enhanced the compressive strength by 764% (from 0.039 to 0.337 MPa). In addition, the thermal conductivity of the ceramics was as low as 0.039 W m^?1 K^?1. Owing to these outstanding characteristics, these porous silica ceramics are expected to be employed as thermal insulation material in diverse fields, especially aerospace and space where weight is an important constraint.     

Preparation of novel reticulated prickly porous ceramics with mullite whiskers

Porous materials are widely used in heat exchangers, sewage treatment, electromagnetic shielding, thermal insulation, gas adsorption, photocatalytic due to their high specific surface area. The specific surface area of materials plays a pivotal role in them. It can be enhanced by increasing the porosity of the material, but the cost of this improvement is reducing the strength of the material. In order to improve performance, it is necessary to increase its surface area without reducing the strength of the material. In this work, mullite porous ceramics with mullite whisker on the inside and outside surfaces structures, which known as prickly porous ceramics(PPCs). They were fabricated using polyurethane foam coated with slurries as the pore-forming agents, sintered after secondary impregnation with silica sol and ammonium fluoroaluminate. The the sintering temperature as well as slurry composition of secondary impregnation were tuned to tailor the strength and surface structures of the PPCs. In addition, the potential of PPCs as high-temperature catalyst supports was demonstrated. Overall, the PPCs demonstrated large surface areas and high mechanical strength. This study paved the way for the fabrication of high-performance porous ceramics.     

Hierarchical cellular scaffolds fabricated via direct foam writing using gelled colloidal particle-stabilized foams as the ink

Hierarchical cellular architectures hold great potential in a vast range of applications due to their superior mechanical properties and multifunctionality. In the present work, hierarchical structures composed of porous struts patterned in the form of quadrangular and triangular honeycombs were fabricated via direct foam writing (DFW) using colloidal particle-stabilized Al₂O₃-MgO-SiO₂ foams as the ink. Hydration process of MgO and subsequent formation of colloidal Mg(OH)₂ network endowed the foam ink with viscoelasticity and high storage modulus. The resulting honeycombs with ultrahigh overall porosity (95.3%) and robust compressive strength (2.5 MPa) can be readily fabricated by DFW. The current work exhibits a significant step toward the scalable production of cellular ceramics with hierarchical architecture for various applications, including tissue scaffolds, catalyst supports, thermal insulation, and lightweight structures.     

Additive manufacturing of SiOC scaffolds with tunable structure-performance relationship

Aiming at optimizing the performance of porous ceramics through structural optimization, this work explored the properties variation achieved by designing different patterns in SiOC log-pile structures fabricated by direct ink writing. Specifically, we investigated the effect of filament diameter, spacing between filaments and angle of deflection between adjacent layers on the compression strength and gas permeability of these structures. Results confirm that mechanical performance could be tuned by designing the structures’ architectural features, such as the spacing between filaments and the angle of deflection between layers, leading to changes in the contact area of filaments belonging to adjacent layers. Permeability decreased with varying angle of deflection from 90 ° to 15 °, due to the higher tortuosity of the flow paths. This enables to optimize the strength and permeability of the structure without reducing the porosity of the component.     

建筑陶瓷装饰技术的现状及发展趋势

简要介绍了建筑陶瓷领域、日用陶瓷和工艺美术陶瓷领域装饰技术的最新进展,着重介绍了引领陶瓷装饰技术发展和最新潮流的意大利、西班牙在这方面的水平和成果,他们为开放的中国从世界陶瓷大国尽快过渡到世界陶瓷强国提供了借鉴和方向。装饰技术的总体水平包括设计、装饰技法、装饰工艺、装饰材料和装饰机械装备等几大方面,其中设计是龙头,它应包括产品的图案设计、造型设计、色彩的搭配、产品的应用及展示设计等多个方面;装饰技法包括平面装饰和立体装饰、平铺和点缀、多种装饰材料的交替和组合应用等;装饰工艺包括布料(多管布料、多次布料、随机布料、微粉和干粒布料),丝网印刷(平面丝网印刷、辊筒印刷、胶辊印刷),各种施釉工艺,抛光,柔抛,釉抛和半釉抛工艺,磨边和水刀切割,拼花工艺等;装饰材料有各种色料、成釉、金属釉、干粒、印油、渗花液、喷墨印刷用耗材等;装饰机械装备包括各种装饰机械和工模具。     

Processing of Particle-Stabilized Wet Foams Into Porous Ceramics

Direct foaming of colloidal suspensions is a simple and versatile approach for the fabrication of macroporous ceramic materials. Wet foams produced by this method can be stabilized by long-chain surfactants or by colloidal particles. In this work, we investigate the processing of particle-stabilized wet foams into crack-free macroporous ceramics. The processing steps are discussed with particular emphasis on the consolidation and drying process of wet foams. Macroporous alumina ceramics prepared using different consolidation and drying methods are compared in terms of their final microstructure, porosity, and compressive strength. Consolidation of the wet foam by particle coagulation before drying resulted in porous alumina with a closed-cell structure, a porosity of 86.5%, an average cell size of 35 μm, and a remarkable compressive strength of 16.3 MPa. On the other hand, wet foams consolidated via gelation of the liquid within the foam lamella led to porous structures with interconnected cells in the size range from 100 to 150 μm. The tailored microstructure and high mechanical strength of the macroporous ceramics can be of interest for the manufacture of bio-scaffolds, thermal insulators, impact absorbers, separation membranes, and light weight ceramics.     

Direct ink writing of cordierite ceramics with low thermal expansion coefficient

Since the application of cordierite ceramics is limited by the disadvantages of traditional preparation techniques, 3D printing technology provides the only choice for the rapid preparation of cordierite ceramics with highly complex structures. In this work, the fabrication of cordierite ceramics with complex structures was achieved by direct ink writing. The near-net-shape of cordierite ceramics was realized by the volume expansion caused by the phase transformation. A cordierite ceramic with an average shrinkage rate of 1.58 % was obtained at 1400 °C. The low shrinkage avoids design and manufacturing procedures carried out for dimensional and alignment errors. In addition, the coefficient of thermal expansion was as low as 1.69 × 10^?6 °C^?1. The effect of configuration on the thermal behavior of cordierite ceramics is understood by analyzing the phase composition and microstructure. The cordierites ink reported in this work offers additional possibilities for the production of novel complex structures.     

First printing of continuous fibers into ceramics

This article reports a novel method for three-dimensional (3D) printing of continuous fibers into ceramics to improve the mechanical properties of printed ceramics, which is difficult in other 3D printing technologies. The ceramics were derived by pyrolysis of thermoplastic ceramic precursor feedstocks, which were prepared by two methods. One is homogeneously mixing thermoplastic resins and ceramic precursors. The feedstocks prepared by this method exhibit good thermoplastic properties and can be extruded into filaments. Ceramics were obtained by heating the feedstocks to 1100°C in argon atmosphere. The ceramics were amorphous and remained stable during 1100-1300°C; at 1400°C they decomposed into β–SiC with simultaneous volatile gas generation. Above 1400°C, their quality decreased significantly due to cracking of ceramic skeletons. The other method is directly heating, extruding and printing the ceramic precursor. The precursors showed good printability and complex ceramic structures were printed with continuous carbon fibers inside. The continuous carbon fibers improved the flexural strength of pyrolytic ceramics, which is about 7.6 times better than that of the ceramics without fibers. The novel method unravels the potential of 3D printing of continuous fibers into ceramics with complex lightweight structures to improve the strength.     

Direct ink writing of aluminum-phosphate-bonded Al2O3 ceramic with ultra-low dimensional shrinkage

Three-dimensional (3D) printing of ceramics has attracted increasing attention in various fields. However, the pyrolysis of organic components used for binding or polymerization in 3D printing commonly causes a large shrinkage (up to 30 %–40 %), high porosity, and cracking or deformation, severely limiting practical applications. In this study, 3D printing of Al₂O₃ ceramic architectures with ultra-low shrinkage is realized by introducing inorganic binder aluminum dihydrogen phosphate (Al(H₂PO₄)₃, AP) as a ceramic precursor. Compared to organic binders, the inorganic AP binder can undergo crystallization conversion, which reduces mass loss during sintering at high temperatures, resulting in low shrinkage. Moreover, AP can be used as a rheological modifier to regulate the printability of the ceramic ink for direct ink writing of Al₂O₃ ceramic architectures, such as wood-piled scaffolds, honeycomb structures, and tubes with high fidelity. The resultant Al₂O₃ structural ceramics sintered at 1250 °C exhibit good mechanical performance and structural integrity. Most importantly, the linear shrinkage of the printed ceramics is less than 5 %, which is several times lower than that of ceramics with organic binders. This study provides a viable strategy for fabricating high-performance ceramic architectures with good dimensional fidelity for practical applications.     

Direct ink writing of 3D piezoelectric ceramics with complex unsupported structures

Piezoelectric ceramic, as a typical smart material, shows great potential in applications of sensing & actuation, smart structure and energy harvesting. However, the use of traditional methods to fabricate complex and high-precision piezoelectric ceramic devices faces huge technical difficulties and high molding costs. Direct ink writing is a typical additive manufacturing technology, but has limited capabilities when preparing ceramic products with complex unsupported structures. In this work, a combined process of direct ink writing (DIW) and secondary shaping of flexible ceramic green body has been developed and proved to produce complex piezoelectric ceramics. The PZT ink shows shear thinning behavior and appropriate viscoelasticity such as moderate viscosity and high storage modulus. The printed green body can be flexibly deformed and the samples after polarization show good piezoelectric properties, with an average d₃₃ up to 265 pC/N. This work demonstrates an attractive method for geometrically complex piezoceramic with unique macro structure due to its simplicity and low cost, and provides a solution to the key problems in the existing manufacturing technology of 3D ceramics.     

R-Curve Behavior and Thermal Shock Resistance of Ceramics

The influence of R -curve behavior of ceramics on the strength degradation associated with thermal shock is explored. Of particular significance for this interdependence is the observed nonlinear stress-strain behavior of materials that exhibit minimal strength degradation under severe thermal shock conditions. These two features, R -curve behavior and nonlinear behavior, are incorporated into a fracture mechanics analysis to provide a framework with which to understand severe thermal shock of ceramics. This analysis enables the estimation of the crack growth due to thermal shocking and also the anticipated strength degradation. The influence of specimen size is also addressed, and it is shown that greater strength degradation is anticipated with increasing specimen size. Experimental results for an alumina-zirconia composite material are presented to support the simple analysis.