J.Am. Ceran.So,901063-1070(2007) DOl:10.l11551-2916.2007.01504.x c 2007 The American Ceramic Society urna Constant Current Electrophoretic Infiltration Deposition of Fiber Reinforced Ceramic Composites Yahua Bao and Patrick S. nichols Ceramic Engineering Research Group, Department of Materials Science and Engineering. McMaster Univers Hamilton, Ontario Canada LSS 4L7 Modified electrophoretic infiltration deposition(EPID)under constant voltage(<10 V) was applied across the electrodes constant current conditions is used to fabricate non-conductive- minimize hydrogen evolution. A single fabric composite formed fiber-reinforced composites from an ethanol suspension, Parti- several minutes. Most EPD samples were very thin(one fiber les are infiltrated through a fiber preform by an electric field fabric, or a few fiber tows, thick). To obtain thick composites and are deposited on the front of the electrode and"backfill(multiple fiber fabrics or fiber tows), electrophoretically deposit through the fiber preform. a uniform morphology is achieved at ed fabrics were stacked and then pressure filtrated, i.e., EPD was the optimum deposition rate. The constant current EPID process is modeled as capillary d limits the application of EPd for complex shapes. To avoid infiltration electrophoresis. Particles "stream"the fiber preform the hydrolysis, a non-aqueous suspension is preferred for EPD due to the repulsive interaction between the fiber filaments and however, a thick composite may not be formed. the particles as both have the same-sign surface charge. Electro- The EPD cell can be modified for electrophoretic infiltration osmotic flow makes no contribution to deposit yield as the net of non-conductive fibers. The latter, as a preform, are attached How across a closed capillary cross section is zero. Hamaker's on the front of an electrode and charged particles in a non- law is extended to electrophoretic infiltration; however, the total aqueous suspension are electrophoretically infiltrated through deposit yield is controlled by particle electrophoresis outside the by an electric field. If the fibers and the particles have the same- capillaries due to the much lower electric field in the suspension. sign surface charge, they repel each other. Thus, the particles The deposit thickness increases linearly with time under opti first reach the electrode surface and deposit, and then "backfill mum current conditions. Too high a deposition rate promotes between the fiber filaments until the matrix extends to the outer entrapment in the depositing green bod fiber preform surface. -This process will be termed"electro- phoretic infiltration deposition(EPID) . Introduction Ohkawa and Elsner patented the fabrication of non-con- BER-REINFORCED ceramic matrix composites(CMCs)are ductive fiber-reinforced composites by constant-voltage EPID promising, light-weight structural materials that combine A high-constant voltage(320 V) was applied to an acetone sus- high-temperature strength, improved fracture toughness, dam- pension and EPid was conducted for 10-20 min. a thick de- problem as complete infiltration of the matrix into the fiber tows method. The green composite density was v. sa microstructure age tolerance, and thermal shock resistance but fabrication is a posit was obtained. Strecker et al. 4 published a crostructure, a reliable, simple, and cost-effective processing method must be developed that completely infiltrates the fibers respectively, the percentage theoretical density of the green com- th matrix precursors posite is approximately 30%, indicating that the green body Several techniques have been used to introduce matrices into prepared in this way is very porous, i. e, not well infiltrated infiltration including sol-gel and polymer precursor approach voltage is initially consumed in the suspension and hence the and electrophoretic deposition(EPD). Both CVI and solu- ultant electric field is very large and the resultant high initial tion infiltration have low penetration efficiency and hence it is deposition rate decreases the efficiency of infiltration, and high- faw concentration is inevitable. Recently, Stoll et al.- reported difficult to obtain a dense green body; it is also difficult by pres- successful fabrication of Nextel 720/A1,O3 composites with up sure filtration. Vibration-assisted infiltration has been reported to fabricate fiber-reinforced porous matrix composites Howev- to four fiber fabrics by EPId under constant voltage due to the same surface charge between the fibers and Al,O3 particles. But er, high-vibration rates can possibly damage the weak layer thick samples still needed to be pressure filtrated coating Since the 1990s, Epd has been explored to fabricate fiber In the present work, the electrophoretic deposition thro reinforced ceramic composites. Conventional wisdon conductive fibers is compared with electrophoretic infiltration suggest that conductive fibers would best serve as the de deposition through non-conductive fibers. It is demonstrated electrode, i. e, the matrix particles deposit directly on t that constant-current EPID can successfully fabricate fiber-re- Carbon fibers. carbon-coated SiC fiber ickel-coated car- inforced composites. The EPId process is modeled via a porous bon fibers, stainless-steel fibers, and polyoyrrole-coated polyethylene board. Under optimum constant current condi- fibers"have been used. Most experiments were conducted in an tons, the deposit yield increases linearly with deposition time. aqueous suspension under a constant voltage. In this case, a low niform fiber composites are achieved with non-conductive fi- ers. Conductive fibers suffer electric field shielding, which se- verely interferes with the deposition process. F. Zok--contributing editor II. Experimental Procedure cript No. 21706. Received April 15, 2006, approved October 30, 2006. TM-DAR alumina (Taimei Chemicals, Tokyo, particle size, 0. 1 um) was dispersed in ethanol with a 1063Constant Current Electrophoretic Infiltration Deposition of Fiber￾Reinforced Ceramic Composites Yahua Bao and Patrick S. Nicholson**,w Ceramic Engineering Research Group, Department of Materials Science and Engineering, McMaster University, Hamilton, Ontario, Canada L8S 4L7 Modified electrophoretic infiltration deposition (EPID) under constant current conditions is used to fabricate non-conductive- fiber-reinforced composites from an ethanol suspension. Parti￾cles are infiltrated through a fiber preform by an electric field and are deposited on the front of the electrode and ‘‘backfill’’ through the fiber preform. A uniform morphology is achieved at the optimum deposition rate. The constant current EPID process is modeled as capillary infiltration electrophoresis. Particles ‘‘stream’’ the fiber preform due to the repulsive interaction between the fiber filaments and the particles as both have the same-sign surface charge. Electro￾osmotic flow makes no contribution to deposit yield as the net flow across a closed capillary cross section is zero. Hamaker’s law is extended to electrophoretic infiltration; however, the total deposit yield is controlled by particle electrophoresis outside the capillaries due to the much lower electric field in the suspension. The deposit thickness increases linearly with time under opti￾mum current conditions. Too high a deposition rate promotes air entrapment in the depositing green body. I. Introduction FIBER-REINFORCED ceramic matrix composites (CMCs) are promising, light-weight structural materials that combine high-temperature strength, improved fracture toughness, dam￾age tolerance, and thermal shock resistance, but fabrication is a problem as complete infiltration of the matrix into the fiber tows and fabrics is difficult. To design properties via controlled mi￾crostructures, a reliable, simple, and cost-effective processing method must be developed that completely infiltrates the fibers with matrix precursors. Several techniques have been used to introduce matrices into fiber preforms, i.e., chemical vapor infiltration (CVI),1 solution infiltration including sol–gel and polymer precursor approach￾es,1 pressure filtration (PF),2 vibration-assisted infiltration,3,4 and electrophoretic deposition (EPD).5–15 Both CVI and solu￾tion infiltration have low penetration efficiency and hence it is difficult to obtain a dense green body; it is also difficult by pres￾sure filtration. Vibration-assisted infiltration has been reported to fabricate fiber-reinforced porous matrix composites. Howev￾er, high-vibration rates can possibly damage the weak layer coating pre-introduced on the fiber surface. Since the 1990s, EPD has been explored to fabricate fiber￾reinforced ceramic composites.16 Conventional wisdom would suggest that conductive fibers would best serve as the deposition electrode, i.e., the matrix particles deposit directly on the fibers. Carbon fibers,5 carbon-coated SiC fibers,6–9 nickel-coated car￾bon fibers,10,11 stainless-steel fibers,12–15 and polyoyrrole-coated fibers17 have been used. Most experiments were conducted in an aqueous suspension under a constant voltage. In this case, a low, constant voltage (o10 V) was applied across the electrodes to minimize hydrogen evolution. A single fabric composite formed in several minutes. Most EPD samples were very thin (one fiber fabric, or a few fiber tows, thick). To obtain thick composites (multiple fiber fabrics or fiber tows), electrophoretically deposit￾ed fabrics were stacked and then pressure filtrated, i.e., EPD was combined with PF.18,19 PF, however, complicates the processing and limits the application of EPD for complex shapes. To avoid the hydrolysis, a non-aqueous suspension is preferred for EPD; however, a thick composite may not be formed. The EPD cell can be modified for electrophoretic infiltration of non-conductive fibers. The latter, as a preform, are attached on the front of an electrode and charged particles in a non￾aqueous suspension are electrophoretically infiltrated through by an electric field. If the fibers and the particles have the same￾sign surface charge, they repel each other. Thus, the particles first reach the electrode surface and deposit, and then ‘‘backfill’’ between the fiber filaments until the matrix extends to the outer fiber preform surface.19–25 This process will be termed ‘‘electro￾phoretic infiltration deposition (EPID).’’ Ohkawa and Elsner22 patented the fabrication of non-con￾ductive fiber-reinforced composites by constant-voltage EPID. A high-constant voltage (320 V) was applied to an acetone sus￾pension and EPID was conducted for 10–20 min. A thick de￾posit was obtained. Streckert et al. 24 published a microstructure of a thick Nicalon-HVR-fabric/SiC composite fabricated by this method. The green composite density was 0.8 g/cm3 . Consider￾ing that the fiber and SiC density are 2.35 g/cm3 and 3.20 g/cm3 , respectively, the percentage theoretical density of the green com￾posite is approximately 30%, indicating that the green body prepared in this way is very porous, i.e., not well infiltrated. Macro-voids exist in the composite due to inefficient particle infiltration. Virtually no particles infiltrate the fiber tows. Most voltage is initially consumed in the suspension and hence the resultant electric field is very large and the resultant high initial deposition rate decreases the efficiency of infiltration, and high- flaw concentration is inevitable. Recently, Stoll et al. 25 reported successful fabrication of Nextel 720/Al2O3 composites with up to four fiber fabrics by EPID under constant voltage due to the same surface charge between the fibers and Al2O3 particles. But thick samples still needed to be pressure filtrated. In the present work, the electrophoretic deposition through conductive fibers is compared with electrophoretic infiltration deposition through non-conductive fibers. It is demonstrated that constant-current EPID can successfully fabricate fiber-re￾inforced composites. The EPID process is modeled via a porous polyethylene board. Under optimum constant current condi￾tions, the deposit yield increases linearly with deposition time. Uniform fiber composites are achieved with non-conductive fi- bers. Conductive fibers suffer electric field shielding, which se￾verely interferes with the deposition process. II. Experimental Procedure TM-DAR alumina (Taimei Chemicals, Tokyo, Japan, particle size, 0.1 mm) was dispersed in ethanol with a polyethyleneimine F. Zok—contributing editor **Fellow, American Ceramic Society. w Author to whom correspondence should be addressed. e-mail: nicholsn@mcmaster.ca Manuscript No. 21706. Received April 15, 2006; approved October 30, 2006. Journal J. Am. Ceram. Soc., 90 [4] 1063–1070 (2007) DOI: 10.1111/j.1551-2916.2007.01504.x r 2007 The American Ceramic Society 1063