《复合材料 Composites》课程教学资源（学习资料）第五章陶瓷基复合材料_electrophoretic deposition.pdf_大学文库

Availableonlineatwww.sciencedirect.com DIRECT E≈RS ELSEVIER Journal of the European Ceramic Society 26(2006)1567-1576 www.elsevier.com/locate/jeurcera Fabrication technologies for oxide-oxide ceramic matrix composites based on electrophoretic deposition E. Stoll a P MahraH-G. Kruger aH. Kern a B.J. C. Thomas.AR. BoccacciniD,* a Institute of Materials Technology. Technical University of ILmenau. D-98684 Ilmenau, Germany b Department of Materials, Imperial College London, Prince Consort Road, London SW72BP. UK Received 29 November 2004: received in revised form 17 March 2005; accepted 19 March 2005 Available online 17 May 2005 Abstract Electrophoretic deposition(EPD) was used to fabricate alumina matrix composites with high volume fraction of woven fibre mat(Nextel M 720)reinforcement in a multilayer structure. Colloidal suspensions of Al,O3 nanoparticles in ethanol medium with addition of 4-hydrobezoic acid were used for EPD. Two different techniques were developed for fabrication of Al2O3 matrix/Nextel TM 720 fibre composites. The first method is a combination of standard EPD of single fibre mats with a subsequent lamination procedure to fabricate the multilayered composite The second method involves the simultaneous infiltration of several( three or more)NextelTM 720 fibre mats by EPD in a tailor-made cell. The mposites exhibit a homogeneous matrix microstructure, characterised by a very high particle packing density and relatively low porosity after sintering at 1300C. The EPD cell allows production of relatively large bodies(10 cm diameter). By combination of the multilayer EPD infiltration and lamination processes developed here, thick ceramic matrix composite components(>10mm thickness)can be fabricated, which opens the possibility of greater industrial application of the materials o 2005 Elsevier Ltd. All rights reserved. Keywords: Suspensions; Composites; Al2O3; Electrophoretic deposition 1. Introduction and fibres 15,16 18-25 The main advantages of Epd over a con- ventional slurry route are the reduced processing times and Continuous fibre-reinforced oxide ceramic matrix com- improved control over green body microstructure. 5,6Aque- posites( CMCs) have attracted significant scientific and tech- ous or non-aqueous suspensions of ceramic(nano)particles nological interest for high temperature structural applications are usually considered for forming the matrix, and both con- in gas turbines, rocket engines, heat exchangers and hot fil- ductive(e.g SiC Nicalon, carbon) and non-conductive(e.g. ters, due to their low specific weight, damage-tolerant be NextelTM)fibres have been used as reinforcement. 8-25In haviour, oxidation resistance and high resistance to cree the case of non-conductive fibres, the fibre weave is placed in front of the deposition electrode and the ceramic deposit expended in the optimisation of CMCs, with particular em- forms on the electrode and grow around and through the fibre phasis on the establishment of reliable and cost effective fab- mat. 5.25 A schema of a typical EPD cell, commonly used for rication procedures. -14 the infiltration of single non-conductive fibre mats, is shown Electrophoretic deposition(EPD)is the process by which in Fig charged particles in a liquid medium move under an applied This paper presents EPD based methods for the fabrication potential towards an oppositely charged electrode and coagu of multilayer NextelTM 720 fibre-reinforced alumina matrix late there to form a stable deposit. -EPD has been used for composites. Two techniques are described, based or the production of CMCs with a variety of ceramic matrices Corresponding author. Tel. +44 207594 6731: fax: +44 20 7594675 (i)EPD of single NextelTM 720 fibre mats and subsequer E- Jmail address: a boccaccini@imperial ac uk(A R. Boccaccini lamination using Al2O3 paste to form the matrix and 0955-2219/S-see front matter 2005 Elsevier Ltd. All rights reserved. doi: 10. 1016/j-jeurceramsoc. 2005.03.251

Journal of the European Ceramic Society 26 (2006) 1567–1576 Fabrication technologies for oxide–oxide ceramic matrix composites based on electrophoretic deposition E. Stoll a, P. Mahr a, H.-G. Kruger ¨ a, H. Kern a, B.J.C. Thomas b, A.R. Boccaccini b,∗ a Institute of Materials Technology, Technical University of Ilmenau, D-98684 Ilmenau, Germany b Department of Materials, Imperial College London, Prince Consort Road, London SW7 2BP, UK Received 29 November 2004; received in revised form 17 March 2005; accepted 19 March 2005 Available online 17 May 2005 Abstract Electrophoretic deposition (EPD) was used to fabricate alumina matrix composites with high volume fraction of woven fibre mat (NextelTM 720) reinforcement in a multilayer structure. Colloidal suspensions of Al2O3 nanoparticles in ethanol medium with addition of 4-hydrobezoic acid were used for EPD. Two different techniques were developed for fabrication of Al2O3 matrix/NextelTM 720 fibre composites. The first method is a combination of standard EPD of single fibre mats with a subsequent lamination procedure to fabricate the multilayered composite. The second method involves the simultaneous infiltration of several (three or more) NextelTM 720 fibre mats by EPD in a tailor-made cell. The composites exhibit a homogeneous matrix microstructure, characterised by a very high particle packing density and relatively low porosity after sintering at 1300 ◦C. The EPD cell allows production of relatively large bodies (10 cm diameter). By combination of the multilayer EPD infiltration and lamination processes developed here, thick ceramic matrix composite components (>10 mm thickness) can be fabricated, which opens the possibility of greater industrial application of the materials. © 2005 Elsevier Ltd. All rights reserved. Keywords: Suspensions; Composites; Al2O3; Electrophoretic deposition 1. Introduction Continuous fibre-reinforced oxide ceramic matrix composites (CMCs) have attracted significant scientific and technological interest for high temperature structural applications in gas turbines, rocket engines, heat exchangers and hot filters, due to their low specific weight, damage-tolerant behaviour, oxidation resistance and high resistance to creep and thermal shock.1–6 Significant research effort is being expended in the optimisation of CMCs, with particular emphasis on the establishment of reliable and cost effective fabrication procedures.1–14 Electrophoretic deposition (EPD) is the process by which charged particles in a liquid medium move under an applied potential towards an oppositely charged electrode and coagulate there to form a stable deposit.15–17 EPD has been used for the production of CMCs with a variety of ceramic matrices ∗ Corresponding author. Tel.: +44 20 7594 6731; fax: +44 20 75946757. E-mail address: a.boccaccini@imperial.ac.uk (A.R. Boccaccini). and fibres.15,16,18–25 The main advantages of EPD over a conventional slurry route are the reduced processing times and improved control over green body microstructure.15,16 Aqueous or non-aqueous suspensions of ceramic (nano)particles are usually considered for forming the matrix, and both conductive (e.g. SiC Nicalon®, carbon) and non-conductive (e.g. NextelTM) fibres have been used as reinforcement.18–25 In the case of non-conductive fibres, the fibre weave is placed in front of the deposition electrode and the ceramic deposit forms on the electrode and grow around and through the fibre mat.15,25 A schema of a typical EPD cell, commonly used for the infiltration of single non-conductive fibre mats, is shown in Fig. 1. This paper presents EPD based methods for the fabrication of multilayer NextelTM 720 fibre-reinforced alumina matrix composites. Two techniques are described, based on: (i) EPD of single NextelTM 720 fibre mats and subsequent lamination using Al2O3 paste to form the matrix and 0955-2219/$ – see front matter © 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.jeurceramsoc.2005.03.251

E Stoll et al. /Joumal of the European Ceramic Society 26(2006)1567-1576 (adjustable posite electrode deposition electrode Aqueous or non aqueous suspension o8 Ceramic particles (usually 10-500 nm) 8°68。。08 Frame for fixing fibre mats to the elctrodode otion of the particles Fig. 1. Schematic representation of the typical EPD cell suitable for the infiltration of non-conductive fibre mats with ceramic particles(positively charged in this schema), for the fabr (ii) simultaneous infiltration of multiple Nextel M 720 fibre equipment(Sonifier 450 Branson Ultrasonic SA, Carong mats with Al2O3 particles by means of a single EPD step Geneve, Switzerland). Subsequently, the suspension was left in a newly developed EPD cell. to rest for 24 h at room temperature before being used for The electrochemical behaviour of the Nextel TM 720 fib 2. Experimental procedures mmersed in ethanol with addition of 4-HBS was charac terised using ESA signal measurements. For this experiment, 2.. Materials desized NextelTM 720 fibres were ground using a ball mill (Type P6, Fritsch Company, Germany) to a fine powder of The fibres used in this work are NextelTM 720(3M mean particle size 1.35 um, with particle sizes varying be- Corporation, St Paul,MN,USA)woven into eight-harness tween 0.5 and 2.5 um, as determined by laser scattering pa satin fabrics 26,27 The woven fabrics contain 400 individ- ticle analysis (Zetasizer, Malvern Instruments GmbH). The ual filaments with diameters between 10 and 12 um. Be- objective of the ESA signal measurements on the powered fore using the fibres for composite fabrication, they were NextelTM fibres was to characterise the surface charge ac- desized by a heat treatment at 700oC in air for 10 min. quired by the fibres when immersed in ethanol and the The 100% a-alumina powder used for the matrix was the fect of the 4-HBS dispersant on the surface charge of the commercial powder AKP-50 (Sumitomo, Chemicals, Tokyo, fibre Japan), which has a particle size distribution between 100 and 300 nm and a BET surface area of 10.6m/g(manufacturer 2.3. Composite processing 2.3.1. General description of the process 2.2. Preparation of suspensions for EPD Two different techniques were developed for the fabrication of the Al2 O3 matrix/Nextel 720 fibre com- Ethanol was chosen as the suspension medium to avoid posites. The first method is a combination of EPD of any formation of porosity in the deposits during EPD single fibre mats(individual layers) with a subsequent lam- due to gas evolution, which usually occurs in EPD from ination procedure to fabricate the multilayered composite aqueous suspensions. 8 According to previous investiga- The second method involves the simultaneous infiltration tions on the electrochemical behaviour of Al2O3 parti- of several (three or more)Nextel M 720 fibre mats by cles in ethanol, 29 suspensions containing an optimised a single EPD step in an advanced tailor-made EPD cell concentration of 25 wt %o Al2O3 powder were prepared. 4- Fig. 2 shows the flow chart describing the basic steps in- ydroxybenzoic acid (4-HBS)was used as dispersant agent volved. The following main processing parameters were aconcentration of 4 wt. of solid content. This was the op- used after a preliminary trial-and-error optimisation ap timised concentration of dispersant found by electronic sonic proach similar to the one discussed in the literature amplitude(ESA)measurements, which showed that Al2O3 constant electric voltage= 100 V and distance between elec particles in ethanol exhibit a positive charge. The suspension trodes =2 cm. In all cases, the CMCs green bodies after ras dispersed and homogenized in high frequency ultrasound EPD were dried in air at room temperature and subsequently

1568 E. Stoll et al. / Journal of the European Ceramic Society 26 (2006) 1567–1576 Fig. 1. Schematic representation of the typical EPD cell suitable for the infiltration of non-conductive fibre mats with ceramic particles (positively charged in this schema), for the fabrication of oxide–oxide ceramic matrix composites. (ii) simultaneous infiltration of multiple NextelTM 720 fibre mats with Al2O3 particles by means of a single EPD step in a newly developed EPD cell. 2. Experimental procedures 2.1. Materials The fibres used in this work are NextelTM 720 (3M Corporation, St. Paul, MN, USA) woven into eight-harness satin fabrics.26,27 The woven fabrics contain ∼400 individual filaments with diameters between 10 and 12 m. Before using the fibres for composite fabrication, they were desized by a heat treatment at 700 ◦C in air for 10 min. The 100% -alumina powder used for the matrix was the commercial powder AKP-50 (Sumitomo, Chemicals, Tokyo, Japan), which has a particle size distribution between 100 and 300 nm and a BET surface area of 10.6 m2/g (manufacturer data). 2.2. Preparation of suspensions for EPD Ethanol was chosen as the suspension medium to avoid any formation of porosity in the deposits during EPD due to gas evolution, which usually occurs in EPD from aqueous suspensions.28 According to previous investigations on the electrochemical behaviour of Al2O3 particles in ethanol,29 suspensions containing an optimised concentration of 25 wt.% Al2O3 powder were prepared. 4- Hydroxybenzoic acid (4-HBS) was used as dispersant agent in a concentration of 4 wt.% of solid content. This was the optimised concentration of dispersant found by electronic sonic amplitude (ESA) measurements, which showed that Al2O3 particles in ethanol exhibit a positive charge. The suspension was dispersed and homogenized in high frequency ultrasound equipment (Sonifier 450 Branson Ultrasonic SA, CarongeGeneve, Switzerland). Subsequently, the suspension was left to rest for 24 h at room temperature before being used for EPD. The electrochemical behaviour of the NextelTM 720 fibre immersed in ethanol with addition of 4-HBS was characterised using ESA signal measurements. For this experiment, desized NextelTM 720 fibres were ground using a ball mill (Type P6, Fritsch Company, Germany) to a fine powder of mean particle size 1.35 m, with particle sizes varying between 0.5 and 2.5m, as determined by laser scattering particle analysis (Zetasizer, Malvern Instruments GmbH). The objective of the ESA signal measurements on the powered NextelTM fibres was to characterise the surface charge acquired by the fibres when immersed in ethanol and the effect of the 4-HBS dispersant on the surface charge of the fibre. 2.3. Composite processing 2.3.1. General description of the process Two different techniques were developed for the fabrication of the Al2O3 matrix/NextelTM 720 fibre composites. The first method is a combination of EPD of single fibre mats (individual layers) with a subsequent lamination procedure to fabricate the multilayered composite. The second method involves the simultaneous infiltration of several (three or more) NextelTM 720 fibre mats by a single EPD step in an advanced tailor-made EPD cell. Fig. 2 shows the flow chart describing the basic steps involved. The following main processing parameters were used after a preliminary trial-and-error optimisation approach similar to the one discussed in the literature30: constant electric voltage = 100 V and distance between electrodes = 2 cm. In all cases, the CMCs green bodies after EPD were dried in air at room temperature and subsequently

E Stoll et al. /Joumal of the European Ceramic Society 26(2006 )1567-1576 Stainless stee AKP-50/Al2O3 (Ethanol) (NexrelTM720 SS)substrate Fibre mat(s) strongly ultrasonically fixed to ss substrate EPD EPD of multilayer (single fibre mat (Three or more fibre mats (air, room temperature) nats) T<80C) “滥 more layers of 20 fibre mats (CMC) aau:08 arT<1300°) ar,T<1300°c) CMC Fig. 2. Flow chart describing the two methods developed to produce ceramic matrix composites(CMCs) with alumina matrix and three or more layers of Nextel TM 720 fibre mats as reinforcement a pressureless sintering process was used to densify the ng polyvinylalcohol(PVA)with a-Al2O3 particles and composites. deionised water according to the composition described in Table 1. The paste coating on wet surfaces of fibre mats previously infiltrated by EPD was applied using a Doc 2.3.2. Process 1: EPD of single fibre mats and subsequent lamination tor Blade type method(see Fig 3). The thickness of the Fibre mats of square shape with an effective area for in- peated for three l: oating was between 0.5 and 1 mm. The procedure was re yers and subsequently the composite(green iltration of 45 mm x 45 mm were used. The stable suspen- body) was consolidated, forming a three-layer"sandwich filt sion was incorporated in a typical(standard)electrophoretic packet, by warm-pressing. The application of heat during deposition cell, as the one shown in Fig. 1. Under the application of the external electrical field, the positively pressing was required to reduce the viscosity of the paste and thus to generate better conditions for impregnation and charged Al2O3 particles in the suspension moved towards the oppositely charged electrode, before which the non- conductive Nextel M 720 fibre mat was placed. The elec- Table 1 tric field of 50 V/cm was kept constant for all experiments Composition of the paste used in the lamination procedure for CMCs fabri and the deposition time was 3 min. Electrophoretically in- cation(see Fig 3) filtrated single fibre mats were dried in air at normal pres- Concentration ure and stored at room temperature in dissicators for later Non-ionized water Owt.%c use Owt.%c icaly the lamination process, the procedure shown schemat- Polyvinilalcohol binder( Polyviol LL 6035) 10-20w%of in Fig. 3 was used. A paste was made by mix- (20% solution

E. Stoll et al. / Journal of the European Ceramic Society 26 (2006) 1567–1576 1569 Fig. 2. Flow chart describing the two methods developed to produce ceramic matrix composites (CMCs) with alumina matrix and three or more layers of NextelTM 720 fibre mats as reinforcement. a pressureless sintering process was used to densify the composites. 2.3.2. Process I: EPD of single fibre mats and subsequent lamination Fibre mats of square shape with an effective area for in- filtration of 45 mm × 45 mm were used. The stable suspension was incorporated in a typical (standard) electrophoretic deposition cell, as the one shown in Fig. 1. Under the application of the external electrical field, the positively charged Al2O3 particles in the suspension moved towards the oppositely charged electrode, before which the nonconductive NextelTM 720 fibre mat was placed. The electric field of 50 V/cm was kept constant for all experiments and the deposition time was 3 min. Electrophoretically in- filtrated single fibre mats were dried in air at normal pressure and stored at room temperature in dissicators for later use. For the lamination process, the procedure shown schematically in Fig. 3 was used. A paste was made by mixing polyvinylalcohol (PVA) with -Al2O3 particles and deionised water according to the composition described in Table 1. The paste coating on wet surfaces of fibre mats previously infiltrated by EPD was applied using a Doctor Blade type method (see Fig. 3). The thickness of the coating was between 0.5 and 1 mm. The procedure was repeated for three layers and subsequently the composite (green body) was consolidated, forming a three-layer “sandwich” packet, by warm-pressing. The application of heat during pressing was required to reduce the viscosity of the paste, and thus to generate better conditions for impregnation and Table 1 Composition of the paste used in the lamination procedure for CMCs fabrication (see Fig. 3) Composition of the paste Concentration Non-ionized water 50 wt.% -Al2O3 (AKP-50) powder 50 wt.% Polyvinilalcohol binder (Polyviol LL 6035) (20% solution) 10–20 wt.% of solid content

E Stoll et al. /Joumal of the European Ceramic Society 26(2006 )1567-1576 (1)Slope for fixing fibre mats (5)Deposition electrode(stainless steel) (7) Strain tensor 4)Electrode(stainless steel) (8)Quick clamp 4. Design of the new electrophoretic deposition cell for the simultaneous infiltration of several Nextel 720 fibre mats:(a) schematic diagram showing position of the cell for vertical deposition, with direction of particles movement opposite to the gravitation force; and (b) schematic diagram showing the I for horizontal deposition direction with additions of the same additive (4-HBS). This curve 3. 2. Fabrication of Al2O3 matrix/NextelM 720 fibre demonstrates that milled Nextel 720 fibres have a pos composites by EPD itive polarity in ethanol suspension. It is also observed that the original value of ESA signal increases from 107 .2.I. Process 1: EPD of single fibre mat and subsequent to 170 m/V for concentrations of 4-HBS of up 0.8 wt % For higher concentrations of 4-HBS, the signal A fibre mat showing high-quality infiltration of Al2O3 par- value stabilized at 170 uPam/V. Thus, at a 4-HBS con- ticles by EPD is shown in Fig 6a. The mean particle size of centration of 4 wt %, chosen for the present study, the the Al2O3 starting powder, in the range 100-300 nm. Is con- fibres and the Al2O3 particles posses the same positive firmed in Fig. 6b, which demonstrates that this particle size polarity, which has advantages regarding the mechanist is appropriate to effectively infiltrate the Nextel 720 fibre of electrophoretic deposition, as discussed below (Section mats. This image qualitatively indicates also the high parti 1) cle packing density in the deposited matrix. The high-quality of the infiltration and the homogeneous matrix microstruc- ture confirm thus the suitability of the suspension compo- sition and the selected concentration of 4-hydroxidbezoic acid. This behaviour is in broad agreement with extensive evidence in the literature on the high versatility of the EPD technique to infiltrate 2D and 3D fibre performs with cerami (nano)particles. 5Ed The SEM micrographs in Fig. 7 compare the microstruc tures of the EPD-infiltrated Nextel720 fibre mat in"green and sintered state. It is possible to observe isolated pores in the sintered matrix. This is an indication that the organic additive 20 EPD suspension has been burned out during the sintering process, leaving some residual porosity. Inspection of Fig. 7b indicates also that the sintering temperature used been too high because some chemical Fig. 5. ESA signal in ethanol suspension of milled Nextel TM 720 fibres as reaction at the fibre/matrix interface is apparent. This effect function of 4-hydroxybenzoic acid concentration. is detrimental for the mechanical properties of the composite

E. Stoll et al. / Journal of the European Ceramic Society 26 (2006) 1567–1576 1571 Fig. 4. Design of the new electrophoretic deposition cell for the simultaneous infiltration of several NextelTM 720 fibre mats: (a) schematic diagram showing the position of the cell for vertical deposition, with direction of particles movement opposite to the gravitation force; and (b) schematic diagram showing the cell for horizontal deposition direction. with additions of the same additive (4-HBS). This curve demonstrates that milled NextelTM 720 fibres have a positive polarity in ethanol suspension. It is also observed that the original value of ESA signal increases from ∼107 to 170Pa m/V for concentrations of 4-HBS of up to 0.8 wt.%. For higher concentrations of 4-HBS, the signal value stabilized at 170 Pa m/V. Thus, at a 4-HBS concentration of 4 wt.%, chosen for the present study, the fibres and the Al2O3 particles posses the same positive polarity, which has advantages regarding the mechanism of electrophoretic deposition, as discussed below (Section 4.1). Fig. 5. ESA signal in ethanol suspension of milled NextelTM 720 fibres as function of 4-hydroxybenzoic acid concentration. 3.2. Fabrication of Al2O3 matrix/NextelTM 720 fibre composites by EPD 3.2.1. Process I: EPD of single fibre mat and subsequent lamination A fibre mat showing high-quality infiltration of Al2O3 particles by EPD is shown in Fig. 6a. The mean particle size of the Al2O3 starting powder, in the range 100–300 nm, is con- firmed in Fig. 6b, which demonstrates that this particle size is appropriate to effectively infiltrate the NextelTM 720 fibre mats. This image qualitatively indicates also the high particle packing density in the deposited matrix. The high-quality of the infiltration and the homogeneous matrix microstructure confirm thus the suitability of the suspension composition and the selected concentration of 4-hydroxidbezoic acid. This behaviour is in broad agreement with extensive evidence in the literature on the high versatility of the EPD technique to infiltrate 2D and 3D fibre performs with ceramic (nano)particles.15,16,18–25 The SEM micrographs in Fig. 7 compare the microstructures of the EPD-infiltrated NextelTM 720 fibre mat in “green” and sintered state. It is possible to observe isolated pores in the sintered matrix. This is an indication that the organic additive used in the EPD suspension has been burned out during the sintering process, leaving some residual porosity. Inspection of Fig. 7b indicates also that the sintering temperature used (1300 ◦C) might have been too high because some chemical reaction at the fibre/matrix interface is apparent. This effect is detrimental for the mechanical properties of the composite

E. Stoll et al. Joumal of the European Ceramic Sociery 26(2006)1567-1576 Fig. 6. SEM micrographs of a Nextel M 720 fibre mat infiltrated with alumina particles by EPD showing:(a)complete and homogeneous infiltration of the NextelTM 720 fibre mat; and(b)high"green"density of the matrix would limit fibre "pull-out"during fracture and the homogeneous microstructure can be obtained, as observed in I would fail in a brittle manner. The possibility of ob- Fig 8b taining an efficient densification of the matrix using shorter sintering time at lower temperatures must be therefore ex- 3. 2.2. Process II: simultaneous EPD of several fibre mats(Nextel 720) Fig. 8a shows a schematic diagram describing the ig. 9 shows a representative SEM micrograph of a sin- nterlocking mechanism of Al2 O3 particles which takes place tered composite fabricated by simultaneous electrophoretic by lamination is shown. During the lamination process at were well infiltrated by the Al2O3 particles In previo V during the warm lamination process. In Fig. 8b, a SEM mi- deposition of four fibre mats, using the cell designed in thi rograph of the microstructure of a composite fabricated study(Fig. 4). The micrograph reveals that the fibre to .80C, Al2O3 particles from the electrophoretically infil- vestigations, the potential of EPD to infiltrate several oxide trated fibre mats and from the paste used for lamination come fibre mats simultaneously has been suggested. However, into close contact. Pores in the" green"matrix are filled by this is the first time that a high-quality infiltration of several AlO particles being pressed together due to the relatively non-conductive fibre mats by ceramic particles using a single low viscosity of the PVA in the paste at 80C. Conse- EPD cycle has been demonstrated, which represents a sub- quently, a compact of high"green"density and relatively stantial improvement in terms of saving processing time and Nextel 720 NextelTM720 Fig. 7. SEM micrographs showing the interface region between a Nextel 720 fibre and the alumina matrix: (a)"green body" and (b) sintered composite (1300° for I h

1572 E. Stoll et al. / Journal of the European Ceramic Society 26 (2006) 1567–1576 Fig. 6. SEM micrographs of a NextelTM 720 fibre mat infiltrated with alumina particles by EPD showing: (a) complete and homogeneous infiltration of the NextelTM 720 fibre mat; and (b) high “green” density of the matrix. since it would limit fibre “pull-out” during fracture and the material would fail in a brittle manner.1 The possibility of obtaining an efficient densification of the matrix using shorter sintering time at lower temperatures must be therefore explored. Fig. 8a shows a schematic diagram describing the interlocking mechanism of Al2O3 particles which takes place during the warm lamination process. In Fig. 8b, a SEM micrograph of the microstructure of a composite fabricated by lamination is shown. During the lamination process at ∼80 ◦C, Al2O3 particles from the electrophoretically infiltrated fibre mats and from the paste used for lamination come into close contact. Pores in the “green” matrix are filled by Al2O3 particles being pressed together due to the relatively low viscosity of the PVA in the paste at ∼80 ◦C. Consequently, a compact of high “green” density and relatively homogeneous microstructure can be obtained, as observed in Fig. 8b. 3.2.2. Process II: simultaneous EPD of several fibre mats (NextelTM 720) Fig. 9 shows a representative SEM micrograph of a sintered composite fabricated by simultaneous electrophoretic deposition of four fibre mats, using the cell designed in this study (Fig. 4). The micrograph reveals that the fibre tows were well infiltrated by the Al2O3 particles. In previous investigations, the potential of EPD to infiltrate several oxide fibre mats simultaneously has been suggested.25 However, this is the first time that a high-quality infiltration of several non-conductive fibre mats by ceramic particles using a single EPD cycle has been demonstrated, which represents a substantial improvement in terms of saving processing time and Fig. 7. SEM micrographs showing the interface region between a NextelTM 720 fibre and the alumina matrix: (a) “green body”; and (b) sintered composite (1300 ◦C for 1 h)

E Stoll et al. /Joumal of the European Ceramic Society 26(2006 )1567-1576 573 Oxide fibre mat lextel 720 High quality Al,o nd al, o, particles between single fibre Electrophoretic lamination technique particles High-quality intra tow Infiltration achieved by EPD Homogeneous AL,O, matrix between (a) Fig. 8.(a) Schematic diagram depicting the mechanism of interlocking of Al2O3 particles during the lamination process between two electrophoretically infiltrated fibre mats; and (b) SEM micrograph of a sintered multilayer composite sample(1300 C for 1 h)consisting of three fibre mats layers cost in comparison with the standard procedure of infiltrating 4. Discussion single fibre mats in different EPD cycles. As Fig. 9 shows, I intra-tow and inter-tow infiltration has been achieved and 4.1. Mechanism of epd of a 203 particles onto oxide a very compact structure with high fibre volume fraction was fibre mats obtained without the need for subsequent processing steps Moreover, it is seen(Fig. 9) that the gap between adjacent In the following, a phenomenological description is pre- fibre mats is 50 um, which is much smaller than that ob- sented of the mechanism of electrophoretic infiltration of ox- tained in the laminated Matrix-rich ide fibre mats by ceramic particles exhibiting the same surface gions, which are prone to microcracking and microstructural charge polarity, as in the present experiments defects, are thus minimised. It should be also pointed out that As schematised in Fig. 10, it is proposed that the total these samples had a diameter of 10 cm, being therefore the trajectory of the particles before reaching the electrode can largest ceramic composite components fabricated by EPD to be divided in two regions. The first region, namely the"ap date, as far as the authors are aware proaching trajectory", occurs in the suspension at a given Fig9. SEM micrograph of a Nextel M 720 fibre-reinforced alumina matrix composite containing four fibre layers(fibre mats) fabricated by simultaneous electrophoretic deposition. The sample was sintered at 1300.C for 1 h

E Stoll et al. /Joumal of the European Ceramic Society 26(2006)1567-1576 Approaching trajectory Fibre Nextel 720 F.: Stroke s friction force 0O Relaxation force m Oscillatory motion of the particle due to particle and fibres Direction of growth of the same charge Repulsion force between fibre and partide with the same charge. Fig 10. Schematic diagram describing the motion of positively charged a-Al2O3 particles as they infiltrate a positively charged Nextel M 720 fibre mat during distance away from the electrodes, where the particles move cles reach the electrode or the surface of previously deposited externally applied electric field. The second region, the"e particles, they have no further possibility to move and so the towards the deposition electrode only under influence of th electrophoretic ceramic deposit grows with a high particle filtration trajectory, occurs close to the deposition electrode packing density. For the case where fibre and particle have here the charge of the fibres influences the motion of the opposite surface charge, on the contrary, it is expected that harged particles. In the ideal case of a stable suspension, coagulation will occur on the first layer of fibres encountered the particles move as separate entities(no agglomeration), by the travelling particle. Consequently, the formation of a and they all move simultaneously in random manner due to deposit on the outer fibre layer will block or at least make e attraction and repulsions forces between them(dVlo- more difficult the movement of the particles towards the in- theory ). A simple linear motion of the particle under the terior of the fibre mat, which could result in poor infiltration external voltage can be assumed in the"approaching trajec- and low quality microstructure of the green bod In the"infiltration trajectory teraction forces appear between particles and the charged 42. Comparison of the two processes fibres. In the present case, where fibres and particles pos sess the same charge, there are repulsion forces(F1) acting Both techniques developed here are convenient routes to between particles and fibres as shown in Fig. 10. For each the manufacture of multilayer NextelTM720fibre-reinforced particle, these forces depend on the relative distance between alumina matrix composites. The method based on the simul- particles and fibres. Due to the applied external electrical taneous Epd of several fibre mats resulted in higher fibre vol field, each positively charged particle is attracted to the fi- ume fraction, higher matrix density and more homogeneous bre mat because this is fixed to the cathode. However, the matrix microstructure than the standard method of epd of particles are repelled before they can reach the fibre surfaces single fibre mats As assessed by SEM, less structural damage (coagulation point) due to the positive charges on the fibres. developed in the matrix during sintering. In addition, damage It can be hypothesised that under the effect of the repulsive was minimised due to less extent of manipulation of the green forces due to the surrounding fibres, the particles will follow body, as the intermediate steps of forming the composite by the path with the fewest possible obstacles until reaching the lamination were eliminated. This benefit becomes apparent next interstice between adjacent fibres. Thus, when the parti- when comparing Figs. &b and 9. Nevertheless, the advantage

1574 E. Stoll et al. / Journal of the European Ceramic Society 26 (2006) 1567–1576 Fig. 10. Schematic diagram describing the motion of positively charged -Al2O3 particles as they infiltrate a positively charged NextelTM 720 fibre mat during EPD. distance away from the electrodes, where the particles move towards the deposition electrode only under influence of the externally applied electric field. The second region, the “in- filtration trajectory”, occurs close to the deposition electrode where the charge of the fibres influences the motion of the charged particles. In the ideal case of a stable suspension, the particles move as separate entities (no agglomeration), and they all move simultaneously in random manner due to the attraction and repulsions forces between them (DVLOtheory).17 A simple linear motion of the particle under the external voltage can be assumed in the “approaching trajectory”. In the “infiltration trajectory”, however, additional interaction forces appear between particles and the charged fibres. In the present case, where fibres and particles possess the same charge, there are repulsion forces (F1) acting between particles and fibres as shown in Fig. 10. For each particle, these forces depend on the relative distance between particles and fibres. Due to the applied external electrical field, each positively charged particle is attracted to the fi- bre mat because this is fixed to the cathode. However, the particles are repelled before they can reach the fibre surfaces (coagulation point) due to the positive charges on the fibres. It can be hypothesised that under the effect of the repulsive forces due to the surrounding fibres, the particles will follow the path with the fewest possible obstacles until reaching the next interstice between adjacent fibres. Thus, when the particles reach the electrode or the surface of previously deposited particles, they have no further possibility to move and so the electrophoretic ceramic deposit grows with a high particle packing density. For the case where fibre and particle have opposite surface charge, on the contrary, it is expected that coagulation will occur on the first layer of fibres encountered by the travelling particle. Consequently, the formation of a deposit on the outer fibre layer will block or at least make more difficult the movement of the particles towards the interior of the fibre mat, which could result in poor infiltration and low quality microstructure of the green body. 4.2. Comparison of the two processes Both techniques developed here are convenient routes to the manufacture of multilayer NextelTM 720 fibre-reinforced alumina matrix composites. The method based on the simultaneous EPD of several fibre mats resulted in higher fibre volume fraction, higher matrix density and more homogeneous matrix microstructure than the standard method of EPD of single fibre mats. As assessed by SEM, less structural damage developed in the matrix during sintering. In addition, damage was minimised due to less extent of manipulation of the green body, as the intermediate steps of forming the composite by lamination were eliminated. This benefit becomes apparent when comparing Figs. 8b and 9. Nevertheless, the advantage

E. Stoll et al. Journal of the European Ceramic Society 26(2006)1567-1576 57: of the method based on single layer EPD and lamination is 5. Peters. P. W. M. Daniels. B. Clements. F and Vogel. W. D. Me that it offers the possibility to produce thick ceramic com- chanical characterisation of mullite based ceramic matrix composites posite plates, without any lin other than the number at test temperatures up to 1200C. J. Eur. Ceram. Soc., 2000, 20 531-535 of extra lamination steps required. Indeed, the lamination of H. Chawla, K. K, Xu, Z. multilayer"green"bodies fabricated by simultaneous EPD Ha, J.S. Thermal degradation of fibre coatings in mullin of several fibre mats, effectively combining both method reinforced mullite composites. J. Am. Cera. Soc., 1997, 80 would lead to even larger and thicker CMC compone 7. Holmquist. M. G. and Lange, F. F, Processing and properti us oxide matrix composite reinforced with continuou Am. Ceram.Soc,2003,86,1733-1740. 5. Conclusions K. A. et aL, Fugitive interfacial carbon coatings for oxide/oxide composites. J. Am. Ceram. Soc., 2000. 83, 329- Two processes for the manufacture of alumina matrix com- 336. posites with multilayer Nextel M 720 fibre reinforcement dense glass and ceramic matrix composites In Comprehensive Com based on EPD were developed and evaluated. Stable suspen- posite Materials, ed. A. Kelly and C. Zweben. Elsevier, 2000, Pp sions of Al]O3 particles(25 wt % )in ethanol were used, with 545-66 controlled addition of 4-hydroxicbenzoic acid as the charg 10. Lewis. M. H, Tye, A, Butler, E. and Al-Dawery, I, Development ing additive. Measurements of the ESA signal of suspen- of interfaces in oxide matrix composites. Key Eng. Mater, 1999. 164-165,351-356 sions have confirmed the importance of obtaining the same 11. Cinibulk, M K, Keller, K. A and Mah, T L, Effect of yttrium alu n of electric charge on both the fibres and particles. The minum garnet additions on alumina-fiber-reinforced porous-alumina first processing method, based on infiltration of single fibre matrix composites. J. An. Ceram. Soc., 2004. 87, 88 mats and subsequent lamination, leads to composites of rel- 12. Lee, P. and Yano, T. The influence of fiber coating conditions on atively high density, however, some microstructural damage the mechanical properties of alumina/alumina composites. Compos. Interfaces, 2004. 11, 1-13. in form of matrix microcracks developed during sintering 13. Lange, F. F, Tu. W. C. and Evans, A. G, Processing of damage. The second method involved the simultaneous infiltration of lerant, oxidation-resistant ceramic matrix composites by a precursor several fibre mats(up to 4)in a single EPD experiment. These infiltration and pyrolisis method. Mater. Sci. Eng. A, 1995, A195 composites exhibit a very homogeneous"green"microstruc- ture, characterised by a very high particle packing density. By 14. Chawla, K. K and Chawla. N, Processing of Ceramic Matrix Com combination of the multilayer EPD infiltration and lamina- osites. ASM Handbook. Vol 21. ASM Intemational. Materials Park OH,2001,pp.589599 tion processes, relatively thick components(10 mm thick- 15. Boccaccini, A R Kaya, C and Chawla, K.K. Use of electrophoretic ess)could be fabricated. The focus of current work is the deposition in the processing of fibre reinforced ceramic and glass optimisation of the densification heat treatment and the mea- matrix composites: a review Composites A, 2001, 32, 997-1006. surement of the mechanical properties of the composites 16. Boccaccini, A.R. and Kaya, C, The use of electrophoretic deposition for the fabrication of ceramic and glass matrix composites. Ceram. Tras.2004.153.57-66 17. Sarkar, P. and Nicholson, P. S, Electrophoretic deposition(EPD): Acknowledgements mechanisms, kinetics, and applicatio to ceramics. J. Am. Ceram. Soc. 1996.79,1987-2002 18. Illston, T.., Doleman, P.A., Butler, E.G., Marquis, P.M., Ponton, C.B., We acknowledge financial of“ Deusche Gilbert, M.. et al. UK Patent no. 9124816.1, November 1991 Forschungsgemeinschaft (DFG) no.KE395/4-3 19. Kaya, C, Kaya, F, Boccaccini, A.R. and Chawla, K. K, Fabrica ES wishes to acknowledge the"Katholischer Akademischer tion and characterisation of Ni-coated carbon fibre-reinforced alu Auslaenderdienst-KAAD, Bonn, Germany, and the Pon- mina ceramic matrix composites using electrophoretic deposition. tific Catholic University of Peru(Lima, Peru) for financial Acta Mater,2001,49,1189-1197 20. Moritz, K. and Mueller, E, Electrophoretic infiltration of woven car bon fibre mats with SiC powder suspensions. Key Eng. Mater., 2002 206-213,193-19 ung, M. Lehmann. J and Ziegler, G Ic matrx References composites. In Electrophoretic Deposition: Fr Is and Ap plications, ed. A. R. Boccaccini, O. van der J 1. Chawla, K. K, Ceramic Matrix Composites(2nd ed. ) Kluwer Aca bot. The Electrochemical Society, Pennington, US, 2002, Pp. 255- demic Press, Norwell (MA), Dordrecht, The Netherlands, 200 2. Marshall, D B. and Davis, J. B, Ceramics for future power generation 22 Manocha, L M, Panchal, C. and Manocha, S, Silica/silica co technology: fiber reinforced oxide composites. Curr. Opin. Solid State ites through electrophoretic infiltration. Effect of processing Mater Sci,2001,5,283-289. tions on densification of composites. Sci. Eng. Comp. Mater 3. Holmquist, M., Lundber, R, Sudre, O, Razzell, A G, Molliex, L, 9,219-230 Benoit, J. et aL, Alumina/alumina composite with a porous zirco- 23. Kooner, S W. S. Watson. C. M.A. and M J. Eur 720/mullite composition. compo Ceram.Soc,2000,20.599-606. trophoretic J. Eur Ceram. Soc. 2000. 20 4. Chawla, K. K, Coffin, C. and Xu, Z.R. Interface engineering in ox 24. Kaya, C, Kaya, F. and Boccaccini, A. R, Elect ide fibre/oxide matrix composites. Int. Mater. Rev., 2000, 45, 165-189 position infiltration of 2-D metal fibre-reinforced cordierite ma

E. Stoll et al. / Journal of the European Ceramic Society 26 (2006) 1567–1576 1575 of the method based on single layer EPD and lamination is that it offers the possibility to produce thick ceramic composite plates, without any limitation other than the number of extra lamination steps required. Indeed, the lamination of multilayer “green” bodies fabricated by simultaneous EPD of several fibre mats, effectively combining both methods, would lead to even larger and thicker CMC components. 5. Conclusions Two processes for the manufacture of alumina matrix composites with multilayer NextelTM 720 fibre reinforcement based on EPD were developed and evaluated. Stable suspensions of Al2O3 particles (25 wt.%) in ethanol were used, with controlled addition of 4-hydroxicbenzoic acid as the charging additive. Measurements of the ESA signal of suspensions have confirmed the importance of obtaining the same sign of electric charge on both the fibres and particles. The first processing method, based on infiltration of single fibre mats and subsequent lamination, leads to composites of relatively high density, however, some microstructural damage in form of matrix microcracks developed during sintering. The second method involved the simultaneous infiltration of several fibre mats (up to 4) in a single EPD experiment. These composites exhibit a very homogeneous “green” microstructure, characterised by a very high particle packing density. By combination of the multilayer EPD infiltration and lamination processes, relatively thick components (>10 mm thickness) could be fabricated. The focus of current work is the optimisation of the densification heat treatment and the measurement of the mechanical properties of the composites. Acknowledgements We acknowledge financial support of “Deusche Forschungsgemeinsachaft (DFG)” (Project no. KE395/4-3). ES wishes to acknowledge the “Katholischer Akademischer Auslaenderdienst—KAAD”, Bonn, Germany, and the Pontific Catholic University of Peru (Lima, Peru) for financial support. References 1. Chawla, K. K., Ceramic Matrix Composites (2nd ed.). Kluwer Academic Press, Norwell (MA), Dordrecht, The Netherlands, 2003. 2. Marshall, D. B. and Davis, J. B., Ceramics for future power generation technology: fiber reinforced oxide composites. Curr. Opin. Solid State Mater. Sci., 2001, 5, 283–289. 3. Holmquist, M., Lundber, R., Sudre, O., Razzell, A. G., Molliex, L., Benoit, J. et al., Alumina/alumina composite with a porous zirconia interphase, processing, properties and component testing. J. Eur. Ceram. Soc., 2000, 20, 599–606. 4. Chawla, K. K., Coffin, C. and Xu, Z. R., Interface engineering in oxide fibre/oxide matrix composites. Int. Mater. Rev., 2000, 45, 165–189. 5. Peters, P. W. M., Daniels, B., Clements, F. and Vogel, W. D., Mechanical characterisation of mullite based ceramic matrix composites at test temperatures up to 1200 ◦C. J. Eur. Ceram. Soc., 2000, 20, 531–535. 6. Schmuecker, M., Schneider, H., Chawla, K. K., Xu, Z. R. and Ha, J.-S., Thermal degradation of fibre coatings in mullite-fibrereinforced mullite composites. J. Am. Ceram. Soc., 1997, 80, 2136– 2140. 7. Holmquist, M. G. and Lange, F. F., Processing and properties of a porous oxide matrix composite reinforced with continuous oxide fibers. J. Am. Ceram. Soc., 2003, 86, 1733–1740. 8. Keller, K. A. et al., Fugitive interfacial carbon coatings for oxide/oxide composites. J. Am. Ceram. Soc., 2000, 83, 329– 336. 9. Bhatti, A. R. and Farries, P. M., Preparation of long-fiber-reinforced dense glass and ceramic matrix composites. In Comprehensive Composite Materials, ed. A. Kelly and C. Zweben. Elsevier, 2000, pp. 645–667. 10. Lewis, M. H., Tye, A., Butler, E. and Al-Dawery, I., Development of interfaces in oxide matrix composites. Key Eng. Mater., 1999, 164–165, 351–356. 11. Cinibulk, M. K., Keller, K. A. and Mah, T. I., Effect of yttrium aluminum garnet additions on alumina-fiber-reinforced porous-aluminamatrix composites. J. Am. Ceram. Soc., 2004, 87, 881–887. 12. Lee, P. and Yano, T., The influence of fiber coating conditions on the mechanical properties of alumina/alumina composites. Compos. Interfaces, 2004, 11, 1–13. 13. Lange, F. F., Tu, W. C. and Evans, A. G., Processing of damagetolerant, oxidation-resistant ceramic matrix composites by a precursor infiltration and pyrolisis method. Mater. Sci. Eng. A, 1995, A195, 145–150. 14. Chawla, K. K. and Chawla, N., Processing of Ceramic Matrix Composites, ASM Handbook, Vol 21. ASM International, Materials Park, OH, 2001, pp. 589–599. 15. Boccaccini, A. R., Kaya, C. and Chawla, K. K., Use of electrophoretic deposition in the processing of fibre reinforced ceramic and glass matrix composites: a review. Composites A, 2001, 32, 997–1006. 16. Boccaccini, A. R. and Kaya, C., The use of electrophoretic deposition for the fabrication of ceramic and glass matrix composites. Ceram. Trans., 2004, 153, 57–66. 17. Sarkar, P. and Nicholson, P. S., Electrophoretic deposition (EPD): mechanisms, kinetics, and applicatio to ceramics. J. Am. Ceram. Soc, 1996, 79, 1987–2002. 18. Illston, T.J., Doleman, P.A., Butler, E.G., Marquis, P.M., Ponton, C.B., Gilbert, M.J. et al., UK Patent no. 9124816.1, November 1991. 19. Kaya, C., Kaya, F., Boccaccini, A. R. and Chawla, K. K., Fabrication and characterisation of Ni-coated carbon fibre-reinforced alumina ceramic matrix composites using electrophoretic deposition. Acta Mater., 2001, 49, 1189–1197. 20. Moritz, K. and Mueller, E., Electrophoretic infiltration of woven carbon fibre mats with SiC powder suspensions. Key Eng. Mater., 2002, 206–213, 193–196. 21. Ordung, M., Lehmann, J. and Ziegler, G., Electrophoretic deposition of silicon powder for production of fibre-reinforced ceramic matrix composites. In Electrophoretic Deposition: Fundamentals and Applications, ed. A. R. Boccaccini, O. van der Biest and J. B. Talbot. The Electrochemical Society, Pennington, US, 2002, pp. 255– 263. 22. Manocha, L. M., Panchal, C. and Manocha, S., Silica/silica composites through electrophoretic infiltration. Effect of processing conditions on densification of composites. Sci. Eng. Comp. Mater., 2000, 9, 219–230. 23. Kooner, S., Westby, W. S., Watson, C. M. A. and Farries, P. M., Processing of Nextel 720/mullite composition. composite using electrophoretic deposition. J. Eur. Ceram. Soc., 2000, 20, 631–638. 24. Kaya, C., Kaya, F. and Boccaccini, A. R., Electrophoretic deposition infiltration of 2-D metal fibre-reinforced cordierite ma-

《复合材料 Composites》课程教学资源（学习资料）第五章 陶瓷基复合材料_electrophoretic deposition

《复合材料 Composites》课程教学资源（学习资料）第五章陶瓷基复合材料_electrophoretic deposition