c00.52es and manufacturing ELSEVIER Composites: Part A 32(2001)997-1006 Use of electrophoretic deposition in the processing of fibre reinforced ceramic and glass matrix composites: a review A R. Boccaccini,, C. Kaya, K.K. Chawla Fachgebiet Werkstottechnik, Technische Universitat ILmenau, PF 100565, D-98684 ILmenau, germany Interdisciplinary Research Centre(IRC) for High Performance Applications School of Metallurgy and Materials, The University of Birmingham, Edgbaston, Birmingham B15 2TT, UK Department of Materials and Mechanical Engineering, University of Alabama at Birmingham, Birmingham, AL 35294 USA Abstract Electrophoretic deposition(EPD) is a simple and cost-effective method for fabricating high-quality green'composite bodies which, after a suitable high-temperature treatment, can be densified to a composite with improved properties. In this contribution, we describe the use of EPD technique in the fabrication of fibre reinforced composites, with an emphasis on composites with glass and ceramic matrices containing metallic or ceramic fibre fabric reinforcement. EPD has been used to infiltrate preforms with tight fibre weave architectures using different nanosized ceramic particles, including silica and boehmite sols, as well as dual-component sols of mullite composition. The principles of the EPD technique are briefly explained and the different factors affecting the epd behaviour of ceramic sols and their optimisation to obtain high infiltration of the fibre preforms are considered. In particular, the EPD fabrication of a model alumina matrix composite reinforced by Ni-coated carbon fibres is presented. The pH of the solution and the applied voltage and deposition time are shown to have a strong infuence n the quality of the infiltration. Good particle packing and a high solids-loading were achieved in most cases, producing a firm ceramic deposit which adhered to the fibres. Overall, the analysis of the published data and our own results demonstrate that EPD, being simple and expensive, provides an attractive alternative for ceramic infiltration and coating of fibre fabrics, even if they exhibit tight fibre weave architectures. The high-quality infiltrated fibre mats are suitable prepregs for the fabrication of advanced glass and ceramic matrix compo- sites for use in heat-resistant, structural components. C 2001 Elsevier Science Ltd. All rights reserved Keywords: A Ceramic-matrix composites(CMCs); E. Prepreg: Electrophoretic deposition 1. Introduction ceramic fabrics, including SiC-based (e.g. Nicalor Nippon Carbon Co., Japan), alumina and aluminosilicate The development of fibre reinforced ceramic and glass woven fibre mats [2-5]. Metallic fabrics are commercially atrix composites is a promising means of achieving light- available also [6] and are made from a variety of metals weight, structural materials combining high-temperature including stainless steel and special alloys(e.g. Hastelloy strength with improved fracture toughness, damage toler- X). These fabrics provide interesting reinforcing elements ance and thermal shock resistance [1]. Considerable for the fabrication of ductile phase reinforced brittle matrix research e ffort is being expended in the optimisation of composites, including glass matrix composites ceramic composite systems, with particular emphasi Ceramic and glass composites incorporating 2D or 3D being placed on the establishment of reliable and cost- fibre reinforcements are particularly prone to exhibiting effective fabrication procedures. In this context, while the uncontrolled microstructures and residual porosity. This is initial efforts were in the fabrication of unidirectional because it is extremely difficult to achieve complete infiltra- composites, they are increasingly shifting towards the tion of the matrix material into the fibre tows(where the more isotropic composite materials reinforced by two- intra-tow openings may be down to the order of s100 nm) dimensional (2D)and three-dimensional (3D) fibre architec- Traditional processing routes for 2D or 3D fibre reinforced tures. The majority of the research undertaken so far on the ceramic matrix composites have disadvantages. In particu 2D reinforcement of ceramics has been conducted using lar, simple slurry infiltration is unable to penetrate tight fibre weaves, while chemical vapour infiltration (CVI is an Corresponding author. Present address: Department of Materials, expensive technology due to the numerous re- infiltration Imperial College, London SW7 2BP, UK steps required and the high-cost equipment involved [4] E-mail address: a boccaccini@ic ac uk(.R. Boccaccini) Electrophoretic deposition(EPD)has been developed in 1359-835X/01/S.see front matter O 2001 Elsevier Science Ltd. All rights reserved. PI:S1359-835X(00)00168-8
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A.R. Boccaccini et al. Composites: Part A 32(2001)997-1006 preforms has been studied theoretically and experimentally Sol particles In the present work, a complete literature review focusing on the particular use of EPd to infiltrate ceramic and metallic fibre preforms with the ultimate goal of fabricating composite materials is presented. Typical EPD experimen- tal procedures and the results achieved are described in detail, taking as example a model alumina matrix composite reinforced by Ni-coated carbon fibres Literature review fbre ureter Table 1 presents an overview of the published work deal- ing with the application of the EPD technique for the fabri Fig. 1 Schematic diagram of the epd cell for obtaining cation of fibre reinforced ceramic and glass matrix conductive fibre mats. The fibre mat the positive ele the composites. Other types of ceramic composite systems. particles in the suspension are negatively charged (e.g. silica such as whisker reinforced composites [16, 17], laminated composites [18-20), composite coatings [21], composites with porous layers [22]and functionally graded materials recent years simple and inexpensive method for [22-24]have been fabricated by the EPD technique More- infiltration of tightly woven fibre over, the use of electrodeposition to coat ceramic fibres with preforms omplete in chnique is based on using nanoscale metals with the aim to fabricate metal matrix composites has ceramic particles in a stable non-agglomerated form(such also been investigated [25, 26]. However, research on these as in a sol or colloidal suspension) and exploiting their net areas will not be reviewed here, this paper being restricted to surface electrostatic charge characteristics while in suspen the use of epd for the fabrication of fibre reinforced sion. On application of an electric field the particles will ceramic and glass matrix composites migrate towards and deposit on an electrode. If the deposi- The feasibility of infiltrating ceramic woven fibre tion electrode is replaced by a conducting fibre preform, the preforms by EPD has been demonstrated for a variety of suspended particles will be attracted into and deposited single and mixed component ceramic sols, as summarised in within it, providing an appropriate means of effectively Table 1. Mainly graphite [22, 27-32, SiC-based infiltrating densely packed fibre bundles. A schematic [4, 7, 22, 33-40], alumina [35, 41-43]and aluminosilicate diagram of the basic Epd cell is shown in Fig. 1 (mullite)37, 44, 45] woven fibre mats have been employed The movement of ceramic sol particles in an aqueous es investigated have been silica, alumina, suspension within an electric field is governed by the field mullite, SiC, Si3 N4 and borosilicate glass. Both aqueous strength, and the pH, ionic strength and viscosity of the and non-aqueous suspensions have been used, although solution [4]. The electrophoretic mobility(EM) of the aqueous colloidal suspensions or sols are preferred due to harged particles in suspension is given by [8] environmental and cost advantages [46]. The experiments U have been invariably carried out in laboratory scale, using EM= E (1) EPD cells of small dimensions, i.e. the gap between the electrodes was between 1 and 5 cm in most studies. and where U is the velocity, E the field strength, e the dielectric the area of the fibre preforms infiltrated was smaller than constant,s the zeta potential and n the viscosity. Accord- 100 cm". When EPD is used as a ceramic forming techni ingly, a suitable suspension for EPD should have high- que, it is possible to use either constant current or constant particle surface charge, high dielectric constant of the liquid voltage conditions. An analysis of the literature showed, phase and low viscosity. Moreover, low conductivity of the however, that all investigations have been conducted by suspending medium to minimise solvent transport is using constant voltage conditions, the reason being most probably that this is the simplest mode of operation The phenomenon of electrophoresis has been known In the case of non-conductive fibres, such as aluminosis since the beginning of the last century [9] and has found ate(mullite)fibres of the type Nextel 720(3M Co., MN extended application in ceramic technology. In available USA)or alumina fibres(e.g. Almax, Mitsui Mining Co comprehensive review articles, complete descriptions of Japan), a modification of the basic EPD cell must the basics of the EPD technique and its applications in conducted. This has been called electrophoretic filtration ceramics have been presented [8, 10-12]. Moreover, the deposition(EFD) and it is a modification of a method deep electrophoretic penetration of porous substrates, used previously by Clasen [47]. Here, both electrodes are which is related to the Epd infiltration of tight fibre made from stainless steel and a filter metallic membrane is
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A.R. Boccaccini et al./Composites: Part A 32(2001)997-1006 diphasic (or mixed) sols(e.g. silica-alumina dual sols of mullite composition), the process becomes more compl cated than with the single species (e.g. single silica or alumina sols). This is because it is necessary to control the mobility and zeta potential of both species in order for both of them to migrate to the same electrode and co-deposit without segregation under EPD conditions. In particular, for the fabrication of mullite matrices, it is necessary to main tain the initial silica-alumina proportion in the deposit material to warrant stoichiometric mullite composition Several authors have shown ways to engineer the surface sPTo84、eeU charge of the particles by the addition of surfactants [44]or to control short range particle-particle interactions and M micrograph of EPD-infiltrated Nicalon'fibre mat using a rheological characteristics of the colloidal suspensions by f mullite Details of the EPD technique used are careful variation of the particle size, solids-loading and pH iginal work [38). A high level of matrix infiltration is seen. It [48, 49]. In the case of diphasic(mixed sols of mullite nown that the deposited material fairly kept the original mulli composition, the pH is chosen so t sitely charged, i.e. the alumina and silica particles are posi tively and negatively charged, respectively. Thus, placed between the deposition electrode and the non heterocoagulated particle clusters are formed, which move onducting fibre preform [35, 41, 42]. On applying a rela- as single, composite particles [38, 43]. An example of a ively high voltage (e.g. 60V for alumina sol [35]), the Nicalon fibre mat infiltrated by a mixed sol of mullite alumina particles migrate and deposit on to the membrane composition using EPD is shown in Fig. 2 [38]. A high from one direction only, through the fibre preform, until a level of matrix infiltration is seen. It was shown in this sufficient matrix thickness which envelopes the preform is work that the deposited material fairly kept the original achieved. The high voltage causes hydrogen evolution at the mullite stoichiometric composition anode but the gas is prevented from becoming part of the One of the most critical processing steps that compact by the presence of the filter membrane. In this way optimised, as emphasised by most authors, is the drying of alumina-alumina [35] and mullite-mullite [45] woven fibre the infiltrated fibre preforms. This is because extensive reinforced ceramic matrix composites could be fabricated. microcracking of the gelled ceramic matrix can occur on An analysis of the published work shows that the quality drying, as usually occurs in sol-gel processing. Cracking of the infiltration also depended strongly on the architecture frequently develops due to the differential shrinkage of the of the fibre preform employed but, in general, EPD was able gel network generating tensile stresses at the surface, which to infiltrate even the very tight woven fibre mats used. The may lead to the catastrophic growth of microscopic flaw parameters of the EPD infiltration []. However, thin films(<1-2 um)can be dried without applied and deposition time, were optimised in the different cracking because the tensile stresses developed when they studies to obtain a high solids-loading in the intra-tow shrink are insufficient to cause the growth of cracks [50] regions and firm, adherent, ceramic deposits. When using Thus, a careful control of the thickness of the matrix mate rials deposited by EPD is required, as highlighted in the literature [4, 35]. Fig. 3 shows the different cracking devel- opment upon drying in two Nicalon fibre mats which have been EPD-infiltrated with mullite composition sol [34]. Th sample with thicker deposit exhibits extensive microcrack- ing, while the optimisation of deposit thickness leads to a minimisation of microcracking The analysis of the literature reveals that when the ePd and drying conditions were optimised, the infiltrated fibre fabrics were of sufficient quality (high infiltration, no macroporosity and minimal microcrack development)to be used as preforms for the fabrication of ceramic or glass 25 mm matrix composites The EPD process has also been successfully applied to infiltrate metallic fibre fabrics. Boehmite. silica and titania Fig. 3. Macrograph showing the development of microcracking in SiC Nicalon fibre mats EPD- infiltrated with mullite composition mixed sol nanoparticles have been used as precursors for the ceramic pon drying. Extensive microcracking is developed in thick deposits(left) matrices [22,,, 52]. In borosilicate and soda-lime glass This is minimised by depositing thin films of 1-2 um thickness(right)[341 matrix composites, EPD infiltration of the metallic fibre
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