Ceramic Preforms Research Articles

Synthesis of Porous SiC Preform and Squeeze Infiltration Processing of Aluminium-SiC Metal Ceramic Composites

Metal-Ceramic Composites with high volume fraction of reinforcement find wide applications in the area of tribology and high temperature resistant components like piston, brake pads, heat shields etc. Most of these components can be made by infiltration processing of porous ceramic preforms. The present investigation is to synthesize porous ceramic preform based on SiC particles using inorganic salt as a pore forming agent and Squeeze infiltration is applied to fabricate the Al-SiC metal-ceramic composites. The direct squeeze infiltration of 6061 aluminum alloy on SiC preform is successfully carried out with the controlled process parameters of initial preform temperature, liquid metal superheat, squeeze pressure and its rate of application, and die temperature. The preform and composites are characterized using XRD, optical microscopy, electron microscopy, and hardness and compression strength. Porous ceramic preform with more than 50% porosity has been fabricated by sodium chloride as pore former. The infiltrated composite have shown uniform and complete infiltration of Aluminium alloy in between SiC particles and posses very high hardness of 147 BHN in as cast condition compared to 57 BHN for the 6061 Al alloy.

Inelastic behavior of the single domain of metal‐ceramic composites with lamellar microstructure

AbstractMetal‐ceramic composites are widely applied in the different brunches of industry. The composites are produced by squeeze‐casting of the ceramic preform by molten aluminum alloy. The lamellar microstructure is obtained during freezing of ceramic suspension. The internal structure of the domains can be controlled via freeze‐casting parameters. The material has high anisotropy level and its effective properties depend on lamella orientation. The aim of this study is numerical simulation of the inelastic behavior of the material and its verification by experiment. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Study on Temperature Change Rule of Sprayed Composite Powders in Flight

The temperature change process of the single sprayed composite powder during the self-reactive spray forming process for preparing the Ti (C,N)-TiB2 ceramic preforms was numerically simulated by means of finite element analysis. The results show that after the sprayed composite powder with grain size of 50μm has entered the flame field for 0.35ms, the surface temperature of it will reach the igniting temperature and the self-propagating high-temperature synthesis (abbr. SHS) reaction will take place. The heating rate of the particle in this period is about 2.82×106°C/s. After the SHS reaction has taken place, the heating rate becomes quicker because of the double function of the flame and the reactive heat release. When the temperature of the sprayed particle is higher than that of the flame, the heat exchange process will turn into heat absorption from heat release, which leads to the great drop of the heating rate (about 1.20×106°C/s). The composite powder completes the reaction in 0.88ms and reaches the highest temperature of 2920°C, which makes it become a ceramic droplet. After the reaction has finished, the droplet cools down quickly from exterior to interior, and the surface temperature of it descends to the theoretic eutectic melting point of the composite ceramics (2620°C) after 0.34ms. Then the droplet begins to solidify at some degree of supercooling and becomes ceramic particle. The numerically simulated results before, during and after the reaction match the water-quenching experiments of the sprayed particle with particle size of 50μm during the corresponding period. It indicates the heat process of the sprayed composite powder on the whole, which is composed of being heated, heat releasing, cooling and solidifying.

In situ mullite foam fabrication using microwave energy

Abstract In situ mullite ceramic foams were fabricated using polymeric sponge replication method from ceramic slurry containing alpha alumina and kaolin mixtures. Ceramic preforms were processed using microwave energy and conventional heating. The sintered foam samples were characterized by SEM and XRD observations, density measurements and compression tests in order to observe the effect of two different sintering techniques on the structure and properties. It was found that the microwave processing was completed in a shorter burning out and sintering cycle and produced structures having higher mullite transformation ratio and fine grains.

Ceramic Preforms with 2D Regular Channels for Fabrication of Metal/Ceramic-Reinforced Composites

Aligned regular 2D channels were fabricated in alumina via two routes: soft metal and carbon fibers. The soft metal route was accomplished employing centrifugal forces to eject the molten metal from the green matrix. The carbon fiber route was accomplished by burning out the carbon fibers between 450°C and 630°C. In both methods, pressureless sintering followed, yielding the desired 2D channel profiles. Some porous preforms exhibited higher fracture strength than the solid specimens, and this has been attributed to the ability of the channels to reduce the population and distribution of cracks in the porous material.

Fabrication and Tribological Properties of High Temperature Self-Lubrication Composites Prepared by Gas-Pressure Infiltration Technique

Powder metallurgy derived microporous Al2O3/FeCrWMoV metal ceramic preforms were infiltrated with 60Pb40Sn based solid lubricants to create almost fully dense self-lubrication composites. By means of scanning electron microscope (SEM) and energy dispersive X-ray spectrometer (EDS), it was found that 60Pb40Sn-based solid lubricants are well dispersed and embedded in the Al2O3/FeCrWMoV matrix. The friction and wear behaviors of the composites sliding against ZrO2 ceramic from ambient to 800 °C were investigated using a pin-on-disk wear tester.The results showed that the composites exhibited self-lubricating properties at elevated temperatures up to 700 °C. The friction coefficients of less than 0.27 at 600 °C and wear rates of 6×10−6 mm3/N m are obtained when rubbing against ZrO2 ceramic under a normal load of 50 N and a sliding speed of 0.139m/s for 2 hours. The occurrences of lower friction coefficient and plateau in wear rate have been related to the formation of a film of lubricant almost covered entirely the substrate beneath.

Complete determination of elastic moduli of interpenetrating metal/ceramic composites using ultrasonic techniques and micromechanical modelling

Abstract The complete stiffness matrices of several metal/ceramic composites were analysed using the complementary ultrasonic spectroscopic techniques ultrasound phase spectroscopy (UPS) and resonant ultrasound spectroscopy (RUS). Three different aluminum/alumina composites having complex interpenetrating architectures were studied: a composite based on freeze-cast ceramic preform, a composite based on open porous ceramic preform obtained by pyrolysis of cellulose fibres, and a composite based on discontinuous fibre preform. Six of the nine independent elastic constants describing orthotropic elastic anisotropy were pre-determined by ultrasound phase spectroscopy and used as initial guess input for resonant ultrasound spectroscopy analysis, making the final results of all nine elastic constants more reliable. In all cases, consistent and reproducible results are obtained. Finally the experimental results were compared with effective elastic constants calculated using micromechanical modelling and a good correspondence between both is obtained.

Processing of Ceramic Preforms for TRIP-Matrix-Composites

Metal matrix composites have been produced by conventional infiltration of ceramic preforms. The magnesia partially stabilised ceramic foams were prepared by replication method. In terms of the present paper the second process step that comprises the cold spraying of the impregnated foam is optimised. The spray coating is essential in ceramic foam production. It eliminates defects that are caused due to the squeezing process and assists to reach the critical wall thickness for acceptable mechanical properties. For this reasons the rheology of the spraying slurry and the adjustment of the spraying system have been investigated. Quality of the spray coatings was evaluated by computer tomography. The obtained ceramic foams were infiltrated by a TRIP-steel (TRansformation Induced Plasticity) to create composite materials with improved mechanical properties. Phase composition of the composite material has been analysed using Electron Backscatter Diffraction Method (EBSD).

Development of Porous Ceramic Preforms Based on Magnesia Partially Stabilised Zirconia with Additions of MgAl2O4, MgO, Al2O3 and Ti

The present paper deals with the development of metal matrix composites with improved mechanical properties based on metastable austenitic TRIP-steel and magnesia partially stabilised zirconia. The ceramic material is characterised regarding the influence of different additives (MgAl2O4, MgO, Al2O3) on the monoclinic/tetragonal/cubic phase composition. First results for the infiltration of ceramic preforms are shown, on the one hand performed by conventional steel casting technology and on the other hand by submerging of preforms in a metal melt using a steel casting simulator.

Vacuum infiltration of copper aluminate by liquid aluminium

This paper studies attained microstructures and reactive mechanisms involved in vacuum infiltration of copper aluminate preforms with liquid aluminium. At high temperatures, under vacuum, the inherent alumina film enveloping the metal is overcome, and aluminium is expected to reduce copper aluminate, rendering alumina and copper. Under this approach, copper aluminate toils as a controlled infiltration path for aluminium, resulting in reactive wetting and infiltration of the preforms. Ceramic preforms containing a mixture of Al 2O 3 and CuAl 2O 4 were infiltrated with aluminium under distinct vacuum levels and temperatures, and the resulting reaction and infiltration behaviour is discussed. Copper aluminates stability ranges depend on vacuum level and oxygen partial pressure, which determine both CuAl 2O 4 and CuAlO 2 ability for liquid aluminium infiltration. At 1100 °C and 0.76 atm vacuum level CuAl 2O 4 is stable, indicating pO 2 above 0.11 atm. Reactive infiltration is achieved via reaction between aluminium and CuAl 2O 4; however, fast formation of an alumina film blocking liquid aluminium wicking results in incipient infiltration. At 1000 °C and 3.8 × 10 −7 atm vacuum level, CuAlO 2 decomposes to Cu and Al 2O 3 indicating a pO 2 below 6.0 × 10 −7 atm; infiltration of the ceramic is hindered by the non-wetting behaviour of the resulting metal alloy. At 1000 °C and 1.9 × 10 −6 atm vacuum level CuAlO 2 is stable, indicating pO 2 above 6.0 × 10 −7 atm. Extensive infiltration is achieved via redox reaction between aluminium and CuAlO 2, rendering a microstructure characterised by uniform distribution of alumina particles amid an aluminium matrix. This work evidences that liquid aluminium infiltration upon copper aluminate-rich preforms is a feasible route to produce Al–matrix alumina-reinforced composites. The associated reduction reaction renders alumina, as fine particulate composite reinforcements, and copper, which dissolves in liquid aluminium contributing as a matrix strengthener.

Minimal compliance design for metal–ceramic composites with lamellar microstructures

Metal–ceramic composites produced by melt infiltration of ceramic preforms are studied in an optimal design context. The ceramic preforms are manufactured through a process of freeze-casting of Al 2O 3 particle suspension. The microstructure of these composites can be presented as distributions of lamellar domains. With local ceramic volume fraction and lamella orientation chosen as the design variables, a minimum compliance optimization problem is solved based on topology optimization and finite element methods for metal–ceramic samples with different geometries and boundary conditions. Micromechanical models are applied for the calculation of the effective elastic properties of the composites. Optimized local lamella orientations and ceramic contents are calculated, and the difference between the initial (specimen with constant ceramic content and orientation) and the optimized designs is analyzed. Significant reductions in absolute values of the maximum, minimum and mean values of strain fields in the optimized structures are observed.

Improvement of the mechanical strength of alumina preforms by coating with montmorillonite/LDH gels

A composite material was prepared from montmorillonite and Mg–Al LDH. These oppositely charged particles form thixotropic gels with distinct flow and micro-structural properties. The stability of the gel was dependent on the montmorillonite/LDH ratio. Novel advanced ceramic materials were designed by coating ceramic preforms with these gels. During calcination these gels decompose to metal oxides, aluminosilicates and spinel. On calcination at 1400 °C, MgO formed from the LDH of the gel reacted with the aluminosilicate formed by the decomposition of the montmorillonite. A non-porous dense matrix was formed with well grown crystals of MgAl 2O 4 spinel embedded in the aluminosilicate matrix. When the ceramic preforms like porous alumina tube were dip coated with the gel and fired at 1400 °C, the molten aluminosilicate infiltrated into the pores of the aluminum oxide carrying spinel crystals. These spinel crystals settled in the pores and increased the mechanical strength of the alumina tubes. The compressive strength was increased by around 94% and the mechanical extension in the z-direction in the coated body by 4% compared to the uncoated counterpart.

Electrochemical deposition of metal ions in porous laser sintered inter‐metallic and ceramic preforms

Purpose – The purpose of this paper is to establish a scientific understanding for electrochemical infiltration of laser sintered (LS) preforms.Design/methodology/approach – Electrochemical deposition techniques were modified to induce infiltration of nickel ions inside porous LS structures with deposition on pore walls.Findings – This novel process is feasible and has the potential to produce fully dense parts. Both conductive and non‐conductive preforms can be infiltrated by this method.Research limitations/implications – Removal of trapped fluids and gases inside the porous structure is one of the major challenges in the described electrochemical infiltration process.Practical implications – This work enables low‐cost production of structural parts. It expands the application base for additive manufacturing, especially laser sintering technology.Social implications – The novel process carried out in this research is energy efficient when compared to state‐of‐the‐art vacuum‐melt infiltration.Originality...

Microstructure Development and Properties of HSS-Based Self-Lubrication Composites

High speed steel based ceramic preforms with three-dimensionally interpenetrated micropores were fabricated using the mixture of TiH2, CaCO3 and stearic acid as pore-forming agent. A self-made vacuum high pressure infiltration furnace was used to infiltrate the preforms with Pb-Sn based solid lubricants to create almost fully dense self-lubrication composites. The microstructure and properties of HSS-based self-lubrication composites were investigated as a function of sintered porosity. A quantitative analysis of microstructure was correlated with crushing strength，microhardness and wear rate to understand the influence of pore size, shape and distribution on mechanical and tribological behavior. Crushing strength and microhardness decreased with an increase in porosity. Meanwhile the decrease in microhardness with increasing porosity was slightly. The friction coefficient of HSS-based self-lubrication composites decreased with increasing the volume fraction of lubricant due to the self-lubrication and unique micropore structure. Within the range of lubricant volume fraction from 0% to 14%, the wear rate of the composites decreased steadily with the increase of lubricant content in the composites. Micropore structure and lubricant volume fraction play an important role in determining wear resistance of the composites whereas the measured bulk properties seem to be of minor importance.

Three-Dimensional Printing of Ti3SiC2-Based Ceramics

In the present work, we explored the feasibility of fabricating Ti3SiC2-based ceramics by a near-net-shape fabrication process of three-dimensional printing (3D printing) combined with liquid silicon infiltration (LSI). The porous ceramic preform was fabricated by 3D printing TiC powder with dextrin as a binder. The heat-treated preforms contained bimodal pore structure with interagglomerate pores (d≈23 μm) and intraagglomerate pores (d≈1 μm). Upon infiltration in Ar atmosphere at 1600°–1700°C for 1 h, silicon melt infiltrated the pores and reacted with TiC to yield Ti3SiC2, TiSi2, and SiC. The effects of silicon content and infiltration temperature on the phase composition of the Ti3SiC2-based composites were also studied. After LSI at 1700°C for 1 h, the composites with an initial TiC:Si mole ratio of 3:1.2 attained a bending strength of 293 MPa, a Vickers hardness of 7.2 GPa, and an electrical resistivity of 27.8 μΩ·cm, respectively.

Effects of Geometric Constraint on Phase Selection and Segregation in Cast TiAl

ABSTRACTSimulations of directional solidification of binary peritectic TiAl alloys through ceramic preforms consisting of narrow straight channels with spacings on the order of the dendritic tip radius were performed with a modified cellular automaton coupled to a finite volume calculation of solute diffusion. Depending upon the channel spacing, the microstructure may be refined after dendritic growth through the preform. As the channel width decreases, the lateral solute diffusion in the liquid is more constrained, changing the morphology of the primary phase from dendritic to cellular. In narrow channels, the liquid concentration gradient ahead of the solid/liquid interface decreases resulted in lower growth velocities and higher undercoolings. For hypo-peritectic TiAl alloys, growth conditions that lead to growth of β dendrites can result in α nucleation and growth in narrow channels due to the geometric constraint on solute diffusion.

Application of the semy‐analytical micromechanical methods for optimization of the elastic response of metal‐ceramic composites

AbstractMetal‐ceramic composites produced by melt infiltration of the ceramic preform were studied. The ceramic preform of these materials is manufactured through freeze‐casting process and the microstructure can be presented as distribution of the lamellar domains. Micromechanical models were used for the calculation of the effective elastic properties of the domains. The minimum compliance problem was solved for sample subjected to the four‐point bending test. The optimal orientation and volume fracture of the micro constituents were identified using different models. The difference between the initial and optimized design was analyzed. The convergence of the provided optimization procedure was very rapid. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Numerical estimation of the thermal expansion of lamellar single domains in metal/ceramic composites

AbstractA porous ceramic preform, the pore structure of which is created via a freeze‐casting technique, is infiltrated with a metal melt via sqeeze‐casting. The microstructure of the obtained metal/ceramic composites has lamellar domains with geometrical characteristics which are dependent on the manufacturing parameters. The aim of our study is to predict the coefficients of thermal expansion of single domains of parallel Al2O3 platelets embedded in Al. For this purpose, a homogenization procedure was employed for microstructure based finite element and micromechanical modeling. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Influence of glass phase on Al 2O 3 fiber-reinforced Al 2O 3 composites processed by slip casting

The present work describes the processing of alumina fiber reinforced alumina ceramic preforms consisting of chopped Al 2O 3 fibers (33 wt%) and Al 2O 3 (67 wt%) fine powders by slip casting. The preforms were pre-sintered in air at 1100 °C for 1 h. A lanthanum based glass was infiltrated into these preforms at 1250 °C for 90 min. Linear shrinkage (%) was studied before and after glass infiltration. Pre-sintered and infiltrated specimens were characterized by scanning electron microscopy, energy dispersive X-ray, X-ray diffraction, porosimetry and flexural strength. The alumina preforms showed a narrow pore size distribution with an average pore size of ∼50 nm. It was observed that introducing Al 2O 3 fibers into Al 2O 3 particulate matrix produced warp free preforms with minor shrinkage during pre-sintering and glass infiltration. It was observed that the infiltration process fills up the pores and considerably improves the strength and reliability of alumina preform.

Microstructure and Interface Strength of MMCs Prepared by Pressureless Ni-Induced Infiltration Using Fe Alloy

Metal matrix composites (MMCs) were produced by Ni-induced pressureless infiltration using Fe alloy. The mainly fabrication process was that Ni and Al2O3 powders mixture was pressed and sintered after milled, and then the sintered Al2O3 ceramics were infiltrated by Fe alloy at 1600°C with 4h holding time. While the SEM and EPMA analyses indicated that the interface between ceramics and Fe alloy reaches a full homogeneity after infiltration and Fe alloy could infiltrate Al2O3 ceramic preforms and the maximum infiltration distance was more than 400 μm. This would increase the strength of interfacial due to excellent bonding interface. The fracture strength is about 63.0 MPa.