Ceramic Preforms Research Articles

Densification of Ceramic Matrix Composite Preforms by Si2N2O Formed by Reaction of Si with SiO2 under High Nitrogen Pressure. Part 2: Materials Properties

Ceramic matrix composites (CMCs) have been prepared and optimized as already described in part I of this paper. The fibrous preform made of Hi-Nicalon S fibers was densified by a matrix composed of Si2N2O prepared inside the CMC by reacting a mixture of Si and SiO2 under high nitrogen pressure. This part describes the oxidation resistance and mechanical properties of the optimized CMC. The CMC submitted to oxidation in wet oxygen at 1400 °C for 170 h exhibited an oxidation gradient from the surface to almost the center of the sample. In the outer part of the sample, Si2N2O, Si3N4 and SiC were oxidized into silica in the cristobalite-crystallized form. The matrix microstructure looks similar to the original one at the center of the sample, while at the surface large pores are observed and the fiber/matrix interphase is consumed by oxidation. The elastic modulus and the hardness measured at room temperature by nano-indentation are, respectively, 100 and 8 GPa. The elastic modulus measured at room temperature by tensile tests ranges from 150 to 160 GPa and the ultimate yield strength from 320 to 390 MPa, which corresponds to a yield strain of about 0.6%. The yield strength identified by acoustic emission is about 40 MPa.

Effects of a hierarchical macroporous–mesoporous structure with a low porosity porous ceramic preform on mechanical properties and Si particle refinement of RBBC composites

In this study, a hierarchical macroporous–mesoporous structure B4C/C preform was prepared via gel-casting, using which the pore structure, as well as the B4C slurry stability, could be adjusted by using B4C powders with varying multimodal particle size distributions. The coarse, medium, and fine particle distributions of the B4C powders, and their effects on mechanical properties of the RBBC composites obtained by liquid Si infiltration were investigated. The results showed that the lowest B4C slurry viscosity and the densest B4C/C preform were obtained at a 6:1:3 ratio of coarse, medium, and fine particles. The Vickers hardness, fracture toughness, and flexural strength of the RBBC composites reached 21 ± 3 GPa, 4.09 ± 0.17 MPa m1/2, and 299 ± 17 MPa, respectively. Furthermore, the lowest residual Si content was 7.22 vol%, and fine residual Si phases had a toughening effect owing to their internal compressive stress.

Al/Al2O3 metal matrix composites produced using magnetic field-assisted freeze-casting of porous ceramic structures

Al/Al2O3 metal matrix composites (MMCs) were produced by metal infiltration of porous ceramic preforms. The porous ceramic preforms were fabricated using the magnetic field-assisted freeze-casting method, resulting in vertically aligned porous channels. Preforms were prepared by freezing an Al2O3/Fe3O4-containing slurry within an applied magnetic field. Vertical alignment of the channels was facilitated by the magnetic response of the Fe3O4 in the slurry during the freezing process. After freezing and sublimation, the ceramic preforms were sintered and then infiltrated with molten A356 Al-based alloy. The mechanical properties of the resulting Al2O3/A356 MMCs were compared to those of bulk Al2O3, bulk Al-based alloy (A356), and porous Al2O3 preforms using micro-indentation testing. The indentation hardness and elastic moduli values of Al2O3/A356 MMCs showed good agreement with the predicted theoretical calculations. This study provides a new approach for the design of MMCs with controlled composition and improved mechanical characteristics.

Simulating Infiltration as a Sequence of Pinning and De-pinning Processes

The infiltration of a non-wetting liquid, such as molten metal, into a porous solid, such as a ceramic preform, is influenced by the wetting angle of the liquid on the solid. The link between local wetting and the minimum pressure required for initiation of infiltration or the pressure required for full preform infiltration can deviate strongly from what one would expect on the basis of elementary thermodynamic considerations or simple geometrical models. In this work, we explain the trends observed in experimental studies of pressure infiltration of molten metal into ceramic preforms by means of a percolation model, in which the pores themselves are given a simple geometric shape. This gives a simple yet rich and realistic treatment of the infiltration process. Specifically, the pop-through pressure necessary to traverse a throat between two neighboring circular (2D) or spherical (3D) pores can easily be calculated and incorporated in a 3D network model of many pores produced by generating a packing of slightly overlapping circles or spheres. The resulting pore structure defines a bond percolation network that agrees overall both with predictions of percolation theory and observations from experiment, and which can be extended to address a range of other aspects of multi-phase flow through porous media.

Co-continuous calcium phosphate/polycaprolactone composite bone scaffolds fabricated by digital light processing and polymer melt suction

Innovative scaffolds consisting of a cartesian mesh of interpenetrated composite struts of polycaprolactone (PCL) and β-tricalcium phosphate (β-TCP) in a core/shell configuration are developed. Photocurable slurries with high solid-loading (40 vol% TCP) and reduced viscosity were produced by adding camphor and used to fabricate ceramic preforms with hollow struts through Digital Light Processing (DLP). After sintering the structures were suction-infiltrated by molten PCL, resulting in co-continuous composite scaffolds. Their mechanical performance was evaluated in compressive and bending tests and analyzed under the light of stress fields calculated by finite element numerical simulations. Toughness of the scaffolds was notably increased after incorporating the polymeric core. The new co-continuous architecture facilitates impregnation and improves the isotropy of the reinforcement provided by the polymeric core over other reported alternatives but increases the stresses in the ceramic. This was compensated, however, by the increased intrinsic strength associated to using a more concentrated feedstock.

2D and 3D in-situ mechanical testing of an interpenetrating metal ceramic composite consisting of a slurry-based ceramic foam and AlSi10Mg

An interpenetrating metal ceramic composite, based on a ceramic foam and an AlSi10Mg light-weight aluminum alloy, is investigated under compressive load. The ceramic preform is produced by mechanical stirring, drying and finally sintering. It has a relative density of approximately 25% and is infiltrated via gas-pressure infiltration with the aluminum alloy. The damage processes during compressive load, as well as an understanding of crack development is in focus of this research and obtained by complementing 2D and 3D characterization methods. Therefore, a 2D surface in-situ investigation setup with an universal testing machine, a digital image correlation and a microscopy setup is used. For 3D investigation, a compression test with an in-situ X-ray computed tomography is developed and carried out to get an understanding of the material crack growth and crack propagation, as well as its failure mechanisms inside the interpenetrating metal-ceramic phase composite. The material shows crack initiations in the ceramic phase parallel to the load direction. Formation of crack clusters is followed then by a change in failure mechanism due to shear stress dominated failure with a macroscopic crack in 45° regarding the load direction. A good-natured failure of the composite could be determined. The combination of the 2D and 3D investigation methods gives an insight into the failure behavior of the interpenetrating composite and thus contributes to the understanding of the failure mechanism beyond the current state of knowledge.

Development status and future of ceramic-metal co-continuous composite material

As a kind of composite material designed by space continuous network configuration, the ceramic-metal co-continuous composite owns some special characteristics such as the resistance of friction and wear, high thermal shock resistance, low thermal expansion coefficient and so on, which make it has broad application prospects. Inside, the intrinsic properties of porous ceramic preforms as the ceramic reinforcement in the co-continuous composite have important impacts on the overall performance of the composite. In this review, the main progress in the current preparation methods and surface modification of porous ceramics are systematically analyzed, and both the preparation technology and the performance research of ceramic-metal co-continuous composite are summarized. Finally, we outline the four major challenges that may be encountered in the future development of ceramic-metal co-continuous composites.

Thermal characterization of halloysite materials for porous ceramic preforms

Purpose: The aim of the study was to investigate the possibility of sintering raw (natural) halloysite and pure halloysite to produce porous ceramic preforms, and determination of sintering temperature based on the results of investigations into thermal effects, linear changes and phase transitions. Design/methodology/approach: Due to mullitisation ability of halloysite at high temperature, alternative applications based on the sintering technology (including the production of reinforcement of metal matrix composites) are being searched for. Pure halloysite and Dunino halloysite were selected for the study. Findings: Pure halloysite, characterized by low impurities, dimensional stability during sintering, softening temperature above 1500ºC and ability to transform into mullite at temperatures above 950ºC could be used as a base for the production of sintered, porous mullite preforms. Research limitations/implications: Presence of impurities in Dunino halloysite, contribute to the shift of the sintering temperature towards lower temperatures and caused a rapid and uncontrolled shrinkage of the sample and the appearance of the softening temperature at 1300ºC. Practical implications: Based on the research of thermal (DTA/TG, linear changes in high-temperature microscopy) and XRD studies it is possible to determine the sintering temperature of pure halloysite to manufacture the porous mullite preforms with open porosity. Originality/value: The received results show the possibility of obtaining the new mullite preforms based on pure halloysite.

Characterisation of mechanical and surface properties of novel biomimetic interpenetrating alumina-polycarbonate composite materials

ObjectiveTo determine the mechanical and surface characteristics of two novel biomimetic interpenetrating phase alumina-polycarbonate (Al2O3-PC) composite materials, comprising aligned honeycomb-like porous ceramic preforms infiltrated with polycarbonate polymer. MethodTwo composite materials were produced and characterised. Each comprised a porous structure with a ceramic-rich (polymer-poor) top layer, graduated through to a more porous ceramic-poor (polymer-rich) bottom layer. In addition, pure polycarbonate and dense alumina specimens were subjected to the same characterisation namely: density, compression, three-point bend, hardness, surface loss and surface roughness testing. Scanning electron microscopy and micro computerised tomography were employed for structural examination. ResultsThree-dimensional aligned honeycomb-like ceramic structures were produced and full interpenetration of the polymer phase was observed using MicroCT. Depending on the ceramic volume in the initial aqueous ceramic suspension, the density of the final interpenetrating composites ranged from 2.64 to 3.01g/cm3, compressive strength ranged from 192.43 to 274.91MPa, flexural strength from 105.54 to 148.47MPa, fracture toughness from 2.17 to 3.11MPa.m½, hardness from 0.82 to 1.52GPa, surface loss from 0.71 to 1.40μm and surface roughness, following tooth brushing, from 0.70 to 0.99μm. Composite specimens showed characteristic properties part way between enamel and polycarbonate. SignificanceThere was a correlation between the initial solid ceramic loading in the aqueous suspension, used to produce the porous ceramic scaffolds, and the subsequent characteristic properties of the composite materials. These novel composites show potential as aesthetic orthodontic bracket materials, as their properties fit part way between those of ceramic, enamel and polycarbonate.

Analysis of Process of Metal Filling of Ceramic Preforms Using Darcy's Law

Analysis of Process of Metal Filling of Ceramic Preforms Using Darcy's Law

FGM based on copper–alumina composites for brake disc applications

Copper–alumina composites of the interpenetrating networks type are interesting materials for many applications because of their properties. On the base of preliminary investigations and practical works, in order to obtain a material with high resistance to friction wear as well as good dissipation of heat generated during work, it was decided that a developed material would be prepared on the base of the Cu–Al2O3 composite, with a graded composition. In this paper, we present the developed method of manufacturing dense copper–alumina FGMs, using ceramic preform with a graded porosity infiltrated with molten copper. The article also presents the full characterization of the obtained materials and mainly the impact of microstructure on the useful properties. The produced gradient material of a Cu–Al2O3 brake disk underwent tribological tests under conditions resembling real conditions. These disks also went through a series of abrasive wear trials at different operation stages. In comparison with the reference material (i.e., grey cast iron), the obtained gradient materials are characterized by a lower degree of wear when retaining a similar coefficient of friction value due to the ceramic phase addition. Additionally, it was found that using the copper-based gradient material guarantees faster heat dissipation from the contact area.

Cellular SiC/Iron Alloy Composite

Cellular SiC/iron alloy composite with a spatial structure of mutually intersecting skeletons created with a porous ceramic preform has not been obtained before, despite promising spectrum of potential uses. We tested the possibility of obtaining such material using a SiC material with an oxynitride bonding and grey cast iron. Porous ceramic preforms were made by pouring the gelling ceramic suspension over a foamed polymer base which was next fired. The obtained samples of materials were subjected to macroscopic and microscopic observations as well as investigations into the chemical composition in microareas. It was found that the minimum width of a channel in the preform, which in the case of pressureless infiltration enables molten cast iron penetration, ranges from 0.10 to 0.17 mm. It was also found that the ceramic material applied was characterized by good metal wettability. Were the channels are wide enough for the metal penetration we observed that the ceramics/metal contact area always has a transition zone in which mixing of both components takes place.

Numerical and Experimental Characterization of Elastic Properties of a Novel, Highly Homogeneous Interpenetrating Metal Ceramic Composite

An interpenetrating aluminum–alumina composite is presented, based on a ceramic foam manufactured via a novel slurry‐based route resulting in a highly homogeneous preform microstructure in contrast to other preform techniques. The metal matrix composite (MMC) is produced by infiltrating the open‐porous ceramic preform with molten aluminum at 700 °C using a Argon‐driven gas pressure infiltration process. The resulting MMC and the primary ceramic foam are investigated both numerically and experimentally in terms of microstructural characteristics. In addition, the mechanical behavior of the material as well as the structural and material interactions on the microscale are investigated. To characterize the MMC regarding mechanical isotropy, elastic properties are determined experimentally via ultrasonic phase spectroscopy (UPS). A fast Fourier transform (FFT) formulation is used to simulate the complex 3D microstructure with reasonable effort based on image‐data gathered from high‐resolution X‐ray computed tomography (CT) scans of the ceramic foam as computational grid. Simulations prove that the material properties are, indeed, considered as highly homogeneous with respect to the material microstructure. A comparison with effective experimental investigations confirms these findings.

On the effects of particle size and preform porosity on the mechanical properties of reaction-bonded boron carbide infiltrated with Al-Si alloy at 950 °C

The infiltration of boron carbide preforms with Al alloys at relatively low temperature prevents the formation of the undesired Al4C3 phase. In the present study the effect of boron carbide powder particle size on the mechanical properties and phase composition of composites infiltrated with Al-20%Si alloys at 950 °C was investigated. According to XRD analysis, the infiltrated composites contain Al8C7B4, AlB2 and AlB12, as well as non-reacted Al and Si that originated from solidification of Al-Si alloy. The presence of small amounts of SiC was noted in specimens fabricated from fine boron carbide powder. No evidence for the formation of non-desired aluminum carbide phase was obtained. Infiltration of ceramic preforms with virtually the same green density generated composites with an elastic modulus and bending strength that continuously decreased from 270 GPa and 405 MPa to 195 GPa and 345 MPa for powder with 90% particles close to 3 μm and powder with 90% particles close to 180 μm, respectively. These results ambiguously confirm that boron carbide particle size strongly affects mechanical properties of reaction-bonded composites infiltrated with Al-Si alloy at 950 °C and reflect the amount of newly formed ceramic phases appearing during infiltration and the presence of defects at the metal-ceramic interface.

Injection Molding of 3-3 Hydroxyapatite Composites.

The manufacturing of ideal implants requires fabrication processes enabling an adjustment of the shape, porosity and pore sizes to the patient-specific defect. To meet these criteria novel porous hydroxyapatite (HAp) implants were manufactured by combining ceramic injection molding (CIM) with sacrificial templating. Varied amounts (Φ = 0–40 Vol%) of spherical pore formers with a size of 20 µm were added to a HAp-feedstock to generate well-defined porosities of 11.2–45.2 Vol% after thermal debinding and sintering. At pore former contents Φ ≥ 30 Vol% interconnected pore networks were formed. The investigated Young’s modulus and flexural strength decreased with increasing pore former content from 97.3 to 29.1 GPa and 69.0 to 13.0 MPa, agreeing well with a fitted power-law approach. Additionally, interpenetrating HAp/polymer composites were manufactured by infiltrating and afterwards curing of an urethane dimethacrylate-based (UDMA) monomer solution into the porous HAp ceramic preforms. The obtained stiffness (32–46 GPa) and Vickers hardness (1.2–2.1 GPa) of the HAp/UDMA composites were comparable to natural dentin, enamel and other polymer infiltrated ceramic network (PICN) materials. The combination of CIM and sacrificial templating facilitates a near-net shape manufacturing of complex shaped bone and dental implants, whose properties can be directly tailored by the amount, shape and size of the pore formers.

Microstructure and mechanical properties of Fe matrix composites reinforced by nickel–chromium double-layer coated ZTAP ceramics

The preparation, microstructure and mechanical properties of ZTA particles reinforced Fe matrix composites (ZTAP/Fe composites) were systematically investigated. The X-ray diffraction (XRD), scanning electron microscopy (SEM) and electron probe microanalysis (EPMA) were used to analyze the microstructure and phase constituents, the hardness (H), Young's modulus (E) and plasticity factor (δA) were determined as well. The nickel-chromium double-layer coated ZTAP of core-shell structure was prepared by electroless plating and multi-arc ion plating technologies. The modified ZTAP is consisted of the α-Al2O3, t-ZrO2, α-Cr and γ-Ni phases. In addition, the compressive strength of ceramic preforms is high due to a compact sintering neck formed among ZTAP during high temperature sintering. The preferred sintering process for ZTA ceramic preforms is determined as 1350 °C + 1 h, in this case the preforms show the remarkable porosity and highest compressive strength which are 27.8% and 35.0 MPa, respectively. The interfacial metallurgical chemical reactions occurred during infiltration casting process, which ensure the excellent metallurgical interfacial bonding of the ZTAP/Fe composites. The interface contains double transition layers, which refer to silicate and CrFe phases, respectively. The H, E and δA of interfacial double transition layers were measured by the nano-indentation method, the values of which are situated between the ZTAP and iron matrix.

Anatase TiO2 powder immobilized on reticulated Al2O3 ceramics as a photocatalyst for degradation of RO16 azo dye

The three-dimensional network of open-celled Al2O3 ceramic supports were first fabricated using a polymeric sponge replication technique. The polyurethane foams soaked with the highly loaded Al2O3 ceramic slurry were drained, slowly dried and sintered at 950 °C to complete the burn out process and to construct the ceramic preforms. They were then carefully soaked again with the moderately loaded Al2O3 slurry and sintered at 1500 °C to increase their strength. Finally, the photocatalyst ceramic powder covering the outer surfaces was placed layer by layer through dipping the rigid Al2O3 supports repeatedly in the slurry of TiO2 powder. The dip-applied TiO2 was sintered eventually at relatively low temperature of 700 °C to prevent phase transformation. The efficiencies of the TiO2 coated Al2O3 samples were evaluated by the photocatalytic degradation of reactive orange 16 (RO16) azo dye molecules dissolved in water. Nearly complete color removals were achieved within 75 min under UVC irradiation.

Interfacial Bonding and Abrasive Wear Behavior of Iron Matrix Composite Reinforced by Ceramic Particles.

Using zirconia toughened alumina (ZTA) particles and Ni–Ti complex powders as raw materials, high-Cr cast iron reinforced by ZTA particles was prepared by an infiltration casting process. A continuous transition layer formed at the interface between ZTA particles and the Cr15 matrix, which proves that there is strong metallurgical interfacial bonding at the interface. The phases in the Ni–Ti layer of the ZTAP/Fe composite were preserved compared with the microstructure of sintered ZTA ceramic preform. The hardness of the Ni3Ti, TiO and AlNi2Ti phases in the interfacial transition layer was measured by the nano-indentation method, which is 12.5 GPa, 16.1 GPa and 9.2 GPa, respectively. The three-body wear resistance of the composite reached 12.6 times that of high-Cr cast iron.

Study of the phase composition of fine-grained tungsten carbide based ceramic materials by x-ray phase analysis

The results of X-ray diffraction analysis of qualitative and quantitative phase composition of powder and solid polycrysral samples of the system a-WC/W 2 C are presented. Powder (nanopowder) samples were obtained by plasmochemical synthesis from tungsten oxide and hydrocarbon. High-density fine-grained structure of ceramics was formed by electropulse plasma sintering (spark plasma sintering) of initial industrial a-WC powders (AlfaAesar). Experimental data were obtained on a Shimadzu XRD-7000 X-ray diffractometer (CuKa, λ = 1.54 A). The optimal modes of X-ray shooting of the ceramic samples based on tungsten carbide are presented. In the absence of reference standards for initial crystalline phases (WC and W2C), quantitative phase analysis was carried out using the reference intensity ratio (RIR) or corundum number (instead of the method of calibration curve). The required quantitative ratios were calculated using the structural parameters of corundum a-Al 2 O 3 and phases a-WC, W 2 C. The results of determining the repeatability of the intensity values were used to select the optimal exposure time and width of the receiving slit of the detector of diffracted X-rays. Study of the effect of the quality of sample preparation on the sensitivity of qualitative X-ray phase analysis showed the feasibility of grinding of the surface of solid ceramic samples and their pre-polishing with a diamond paste (grain size not less than 5/3 pm). The accuracy of quantitative phase analysis of powder and sintered ceramic samples was evaluated. The layer-by-layer phase analysis of the ceramic preform revealed a preferential crystallite orientation (texture) in the surface layer and the absence of the impurity phase W 2 C. The sensitivity of X-ray phase analysis to the content of a-W 2 C phase in nanopowders of tungsten monocarbide has been estimated.

Application of highly sensitive spectrophotometric analysis in detection of metal content in molybdenum reinforced alumina obtained by precursor infiltration of ceramic preforms

The competitive method for the preparation of molybdenum reinforced alumina has been proposed and investigated as a model for obtaining metal reinforced ceramics. The proposed method consists of infiltration of porous ceramic preform with a solution of metallic precursor followed by sintering combined with the reduction of deposited salt. This method enables formation of the composites that exhibit 36% improvement in compressive strength and no significant change in Vickers hardness in comparison to pure alumina with addition of only 0.22 wt% of molybdenum. Obtained results showed that the deposited metal concentration is highly correlated with the concentration of the precursor solution. In order to precisely determine the amount of molybdenum in the samples unconventional and novel method based on the UV/VIS spectrophotometry has been developed. This method shows a good detection ability that is suitable for determination of small amounts of metal below 0.5 wt% - a quantity difficult to analyse by using classic methods such as energy-dispersive X-ray spectroscopy (EDS).