COMPOSITES SCIENCE AND TECHNOLOGY ELSEⅤIER Composites Science and Technology 61(2001)1813-1820 www.elsevier.com/locate/compscitech Processing and performance of Nicalon Blackglas and Nextel Blackglas using cure-on-the-fly filament winding and preceramic polymer pyrolysis with inactive fillers Ali Yousefpour, Mehrdad N. Ghasemi Nejhad= Advanced Materials Manufacturing Laboratory, Department of Mechanical Engineering, University of Hawaii at Manoa, 2540 Dole Street Holmes Hall 302. Honolulu. HI 96822. USA Received in revised form 26 April 2001: accepted 8 May 2001 Abstract The effects of inert powder inclusion on processing and mechanical performance of Nicalon/ Blackglas and Nextel Blackglas prepared by cure-on-the-fly filament winding with preceramic polymer pyrolysis have been investigated. Ceramic fiber reinforce- ments were boron-nitride-coated Nextel and carbon-coated Nicalon M. BlackglasTM preceramic polymer was mixed with the micron size inert fillers in the presence of a surfactant agent, Hypermer PS2, to achieve a good dispersion of the powder during the process. Nextel/ Blackglas, Nextel/Blackglas-TiN, Nextel/ Blackglas-TiC, Nextel/ Blackglas-SiC, Nextel/ Blackglas-Si3N4, Nicalon, Blackglas, Nicalon/ Blackglas-TiN, and Nicalon/Blackglas-Si3Na tubes were manufactured. Scanning electron microscopy revealed the good quality of the parts. Samples with fillers exhibited excellent shape retention by co on with those without fillers. C-ring tests were performed to evaluate the mechanical performance of the C-rings at room temperature. The production rate of samples composed of Nextel and Nicalon/filler increased by 14-28%. The strength and displacement to failure dropped by 6-28% and 5- 33%, respectively, for Nextel-based samples, and the same values for Nicalon-based samples were 22-33% and 30-46%, respectively No conclusive statement could be made for modulus. Effects of material system were studied and the results revealed that samples composed of BN-NextelB showed better mechanical performance over samples composed of C-NicalonTM. C 2001 Elsevier Scienc Ltd. All rights reserved Keywords: A. Ceramic matrix composites; A. Preceramic polymer; E Filament winding: Inactive particles; C-ring test 1. Introduction between fiber and matrix are important parameters that control the mechanical properties of CFCCs [6-8]. The recent years, there has been increased interest in fracture toughness of CF CCs is mainly affected by the oughening ceramic-matrix composites (CMCs) by matrix microcracking, fiber/matrix debonding, fiber reinforcing with continuous ceramic fibers such as sili- breakage, work necessary to pull broken fibers out of con carbide (SiC) and silicon nitride(Si3 N4) ceramic the matrix, and frictional sliding resistance between fibers [1-4]. Continuous-fiber ceramic composites fiber and matrix. The fiber /matrix interface properties and relatively high fracture toughness are promising properties, and particularly the fracture toughnesyoe (CFCCs) with nearly non-catastrophic mode of failure and performances have strong influences on mechanica candidate materials for high-temperature structural CMCs [9-11]. Low fracture toughness in CMCs applications such as aircraft structures, hot-gas nozzles, obtained when a strong interfacial bond and large slid- and jet-engine components where a higher inlet tem- ing resistance exist between fiber and matrix. The result perature(a design constraint) is desirable [5, 6]. High- is a brittle failure behavior of the CMC owing to the strength fibers, matrix materials, processing conditions, lack of energy absorption and stress-relieving mechan- fiber/matrix interphase region, and shear strength isms in the manufactured parts [12-14]. The creation of a suitable micro-layer inter-phase between the fiber and matrix is one of the most reliable solutions for the design and control of the fiber/matrix interface and 0266-3538/01/ S.see front matter C 2001 Elsevier Science Ltd. All rights reserved. PII:S0266-3538(01)00066-5
Processing and performance of Nicalon/Blackglas and Nextel/ Blackglas using cure-on-the-fly filament winding and preceramic polymer pyrolysis with inactive fillers Ali Yousefpour,Mehrdad N. Ghasemi Nejhad* Advanced Materials Manufacturing Laboratory, Department of Mechanical Engineering, University of Hawaii at Manoa, 2540 Dole Street, Holmes Hall 302, Honolulu, HI 96822, USA Received in revised form 26 April 2001; accepted 8 May 2001 Abstract The effects of inert powder inclusion on processing and mechanical performance of Nicalon/Blackglas and Nextel/Blackglas prepared by cure-on-the-fly filament winding with preceramic polymer pyrolysis have been investigated. Ceramic fiber reinforcements were boron-nitride-coated Nextel1 and carbon-coated NicalonTM. BlackglasTM preceramic polymer was mixed with the micron size inert fillers in the presence of a surfactant agent,Hypermer PS2,to achieve a good dispersion of the powder during the process. Nextel/Blackglas,Nextel/Blackglas–TiN,Nextel/Blackglas–TiC,Nextel/Blackglas–SiC,Nextel/Blackglas–Si3N4,Nicalon/ Blackglas,Nicalon/Blackglas–TiN,and Nicalon/Blackglas–Si3N4 tubes were manufactured. Scanning electron microscopy revealed the good quality of the parts. Samples with fillers exhibited excellent shape retention by comparison with those without fillers. C-ring tests were performed to evaluate the mechanical performance of the C-rings at room temperature. The production rate of samples composed of Nextel and Nicalon/filler increased by 14–28%. The strength and displacement to failure dropped by 6–28% and 5– 33%,respectively,for Nextel-based samples,and the same values for Nicalon-based samples were 22–33% and 30–46%,respectively. No conclusive statement could be made for modulus. Effects of material system were studied and the results revealed that samples composed of BN-Nextel1 showed better mechanical performance over samples composed of C-NicalonTM. # 2001 Elsevier Science Ltd. All rights reserved. Keywords: A. Ceramic matrix composites; A. Preceramic polymer; E. Filament winding; Inactive particles; C-ring test 1. Introduction In recent years,there has been increased interest in toughening ceramic-matrix composites (CMCs) by reinforcing with continuous ceramic fibers such as silicon carbide (SiC) and silicon nitride (Si3N4) ceramic fibers [1–4]. Continuous-fiber ceramic composites (CFCCs) with nearly non-catastrophic mode of failure and relatively high fracture toughness are promising candidate materials for high-temperature structural applications such as aircraft structures,hot-gas nozzles, and jet-engine components where a higher inlet temperature (a design constraint) is desirable [5,6]. Highstrength fibers,matrix materials,processing conditions, fiber/matrix interphase region,and shear strength between fiber and matrix are important parameters that control the mechanical properties of CFCCs [6–8]. The fracture toughness of CFCCs is mainly affected by the matrix microcracking,fiber/matrix debonding,fiber breakage,work necessary to pull broken fibers out of the matrix,and frictional sliding resistance between fiber and matrix. The fiber/matrix interface properties and performances have strong influences on mechanical properties,and particularly the fracture toughness,of CMCs [9–11]. Low fracture toughness in CMCs is obtained when a strong interfacial bond and large sliding resistance exist between fiber and matrix. The result is a brittle failure behavior of the CMC owing to the lack of energy absorption and stress-relieving mechanisms in the manufactured parts [12–14]. The creation of a suitable micro-layer inter-phase between the fiber and matrix is one of the most reliable solutions for the design and control of the fiber/matrix interface and 0266-3538/01/$ - see front matter # 2001 Elsevier Science Ltd. All rights reserved. PII: S0266-3538(01)00066-5 Composites Science and Technology 61 (2001) 1813–1820 www.elsevier.com/locate/compscitech * Corresponding author
l814 A. Yousefpour, M.M. Ghasemi Nejad/ Composites Science and Technology 61(2001)1813-1820 hence the mechanical performance in CMCs [8, 15]. The 2. Composite material systems inter-phase sufficiently weakens the fiber/matrix bond ing, yields optimum interfacial shear resistance, and Blackglas TM is a siloxane backbone preceramic poly- protects the fiber from the notch and crack-tip effects. mer that can be converted to silicon carboxide(si-C-o) The result is a high fracture toughness and non-cata- ceramic upon pyrolysis. The final ceramic matrix has strophic mode of failure [16, 17] typical composition of 24 wt. carbon(C), 47 wt% Filament winding is an automated and cost-effective silicon (Si), 28 wt. oxygen (O), less that 0. 4 wt% manufacturing technique for producing composite mate- hydrogen(H) and less than 0.1 wt. nitrogen(N) and a rials [18]. Cure-on-the-fly filament winding and pre- density of 2.2 g/cm[24]. Blackglas M has a low density, fabricating CFCCs [19, 20]. In this method, preceramic in common organic solvents, adjustability in curing time polymer is partially cured by in situ heat sources that are from a few minutes to several hours, availability in liquid set up around the mandrel. The partial cure minimizes and B-stage resin form, and ease of manufacturing [24] he migration of the fibers from top layers to bottom Its pyrolysis temperature is between 900 and 1200C in ones, which can otherwise occur because of the winding an inert environment such as argon(Ar)or nitrogen(N) tension build-up through the thickness of the component. Table 1 shows the physical properties of BlackglasTM. This fiber migration often leads to a variation of density Boron-nitride-coated Nextel (BN-Nextel )312 and and fiber volume fraction through the thickness of the carbon-coated NicalonM(C-NicalonTM)fibers were parts. Hence, uniform parts can be manufactured by chosen as the fiber reinforcements. These fibers have initiating cure while winding, in effect, locking the fibers in desirable mechanical performances [25, 26](see Table 2) place during the winding, thereby, achieving reduced fiber The coating thickness and filament diameter of the fiber migration and fiber waviness. As a result, the cure-on-the- reinforcements were I and 10-12 um, respectively fly filament winding technique yields parts with reduced Hypermer polymeric surfactant agent PS2 is a product fiber migration and waviness, enhanced structural uni- of ICI Surfactants Company. Hypermer is designed for formity, better mechanical performances, higher pro- the use in both aqueous and non-aqueous systems, and duction rates, and lower costs [19, 20] has hydrophilic and hydrophobic units in its composi Polymer precursor pyrolysis processing is one of the tion [27]. Hypermer PS2 surfactant agent was mixed with techniques for fabricating CFCCs [21]. It consists of two preceramic polymer to provide good powder dispersion steps. The first step is the fabrication of a polymer- in BlackglasTM. The inert fillers or powder inclusions impregnated part at low temperature, by the use of tra- were ceramic micron-size powders such as SiC, Si3N ditional polymer processing techniques, and the second TiC, and TiN. Table 3 gives the specification of the inert step is the pyrolysis of the part in a high-temperature powder inclusions [28, 291 furnace, as opposed to chemical vapor infiltration(CVi) where the entire process takes place at high temperature [22]. The polymer of the cured parts convert into a 3. Manufacturing procedure ceramic at the pyrolysis step. The major drawback of using the preceramic polymer pyrolysis method to form The manufacturing of continuous-fiber ceramic com- ceramics is its extensive shrinkage [21]. Reinfiltration/ posites( CFCCs) with particle filled matrix using cure- pyrolysis cycles are necessary to reduce the porosity on-the-fly filament winding and preceramic polymer content and increase the density. The density increasing pyrolysis consisted of four steps: (1)preparation of the processes lead to extensive matrix cracking in compo- particle filled preceramic polymer, (2)fiber impregna- sites. Linear shrinkage of more than 25-30% occurs, tion, (3)cure-on-the-fly winding, and(4) pyrolysis/rein- which usually causes extended cracking and voids crea- filtration. Fig. I shows the CFCC particle filled matrix tion in the pyrolyzed products [21, 23]. One possible fabrication methodology using the cure-on-the-fly fila- solution of reducing the excessive shrinkage and porosity ment winding technique creation during pyrolysis is adding filler particles in the In the first step, surfactant agent PS2, in the amount polymer Filler particles could be micron-size inert pow- equal to 5 wt of the selected powder, was added to ders such as silicon carbide(Sic), silicon nitride(Si3N4), titanium carbide(TiC), and titanium nitride(TiN). Inert Table I particles such as ceramic powders do not undergo a che- Physical properties c f BlackglasTM mical reaction with polymer during the pyrolysis. The primary objectives of this work were to study the effects Property of inert-powder inclusion on the processing time and Density(g/cm) mechanical performance of CF CCs manufactured by Temperature stability in air(C) preceramic polymer pyrolysis and cure-on-the-fly fila 2.5-3.59 Viscosity(cps) ment winding
hence the mechanical performance in CMCs [8,15]. The inter-phase sufficiently weakens the fiber/matrix bonding,yields optimum interfacial shear resistance,and protects the fiber from the notch and crack-tip effects. The result is a high fracture toughness and non-catastrophic mode of failure [16,17]. Filament winding is an automated and cost-effective manufacturing technique for producing composite materials [18]. Cure-on-the-fly filament winding and preceramic polymer pyrolysis is a novel technique for fabricating CFCCs [19,20]. In this method, preceramic polymer is partially cured by in situ heat sources that are set up around the mandrel. The partial cure minimizes the migration of the fibers from top layers to bottom ones,which can otherwise occur because of the winding tension build-up through the thickness of the component. This fiber migration often leads to a variation of density and fiber volume fraction through the thickness of the parts. Hence,uniform parts can be manufactured by initiating cure while winding,in effect,locking the fibers in place during the winding,thereby,achieving reduced fiber migration and fiber waviness. As a result,the cure-on-the- fly filament winding technique yields parts with reduced fiber migration and waviness,enhanced structural uniformity,better mechanical performances,higher production rates,and lower costs [19,20]. Polymer precursor pyrolysis processing is one of the techniques for fabricating CFCCs [21]. It consists of two steps. The first step is the fabrication of a polymerimpregnated part at low temperature,by the use of traditional polymer processing techniques,and the second step is the pyrolysis of the part in a high-temperature furnace,as opposed to chemical vapor infiltration (CVI) where the entire process takes place at high temperature [22]. The polymer of the cured parts convert into a ceramic at the pyrolysis step. The major drawback of using the preceramic polymer pyrolysis method to form ceramics is its extensive shrinkage [21]. Reinfiltration/ pyrolysis cycles are necessary to reduce the porosity content and increase the density. The density increasing processes lead to extensive matrix cracking in composites. Linear shrinkage of more than 25–30% occurs, which usually causes extended cracking and voids creation in the pyrolyzed products [21,23]. One possible solution of reducing the excessive shrinkage and porosity creation during pyrolysis is adding filler particles in the polymer. Filler particles could be micron-size inert powders such as silicon carbide (SiC),silicon nitride (Si3N4), titanium carbide (TiC),and titanium nitride (TiN). Inert particles such as ceramic powders do not undergo a chemical reaction with polymer during the pyrolysis. The primary objectives of this work were to study the effects of inert-powder inclusion on the processing time and mechanical performance of CFCCs manufactured by preceramic polymer pyrolysis and cure-on-the-fly filament winding. 2. Composite material systems BlackglasTM is a siloxane backbone preceramic polymer that can be converted to silicon carboxide (Si–C–O) ceramic upon pyrolysis. The final ceramic matrix has typical composition of 24 wt.% carbon (C),47 wt.% silicon (Si),28 wt.% oxygen (O),less that 0.4 wt.% hydrogen (H) and less than 0.1 wt.% nitrogen (N) and a density of 2.2 g/cm3 [24]. BlackglasTM has a low density, a controllable coefficient of thermal expansion,solubility in common organic solvents,adjustability in curing time from a few minutes to several hours,availability in liquid and B-stage resin form,and ease of manufacturing [24]. Its pyrolysis temperature is between 900 and 1200 C in an inert environment such as argon (Ar) or nitrogen (N). Table 1 shows the physical properties of BlackglasTM. Boron-nitride-coated Nextel1 (BN-Nextel1) 312 and carbon-coated NicalonTM (C-NicalonTM) fibers were chosen as the fiber reinforcements. These fibers have desirable mechanical performances [25,26] (see Table 2). The coating thickness and filament diameter of the fiber reinforcements were 1 and 10–12 mm,respectively. Hypermer polymeric surfactant agent PS2 is a product of ICI Surfactants Company. Hypermer is designed for the use in both aqueous and non-aqueous systems,and has hydrophilic and hydrophobic units in its composition [27]. Hypermer PS2 surfactant agent was mixed with preceramic polymer to provide good powder dispersion in BlackglasTM. The inert fillers or powder inclusions were ceramic micron-size powders such as SiC,Si3N4, TiC,and TiN. Table 3 gives the specification of the inert powder inclusions [28,29]. 3. Manufacturing procedure The manufacturing of continuous-fiber ceramic composites (CFCCs) with particle filled matrix using cureon-the-fly filament winding and preceramic polymer pyrolysis consisted of four steps: (1) preparation of the particle filled preceramic polymer,(2) fiber impregnation,(3) cure-on-the-fly winding,and (4) pyrolysis/rein- filtration. Fig. 1 shows the CFCC particle filled matrix fabrication methodology using the cure-on-the-fly filament winding technique. In the first step,surfactant agent PS2,in the amount equal to 5 wt.% of the selected powder,was added to Table 1 Physical properties of BlackglasTM Property Value Density (g/cm3 ) 1.1 Temperature stability in air ( C) 1,200 Coefficient of thermal expansion (106 / C) 2.5–3.59 Viscosity (cps) 5–149 1814 A. Yousefpour, M.N. Ghasemi Nejhad / Composites Science and Technology 61 (2001) 1813–1820
A. Yousefpour, M.M. Ghasemi Nejad/ Composites Science and Technology 61(2001)1813-1820 Impregnation Roller Physical properties of Nicalon M and Nextel B 312 fibers Pre-im Tensioner Rollers operty Nextel 312 Sensing Unit(Cab Coefficient of thermal expansion Preceramic Polymer Tensile strength(GPa) Elastic modulus(GPa) Strain to failure(%) Particle Filled Preceramic polymer Resin Bath 10-12 Fig. 2. Tensioner assembly and particle filled preceramic polymer resin bath Table Specifications of the inert powder inclusions Property TIN mechanically to apply constant tension of 8.89 N to the Nextel fiber tow and 1115n to the Nicalon TM fiber Density(g/cm) 3.18 .22 Particle size range(pm)0.3-1.20.25-1.30.8-1.21.0-1.5 tow. These values were determined experimentally dur Mean particle size (um) 0.5 ing the fabrication of CFCCs 950 In the third step, the impregnated fiber tows were Stability in the ai Stable Stable Stable Stable guided through the pay-out eye system which consisted of 8 rollers and a semi-circular D-ring. The use of the rollers and semi-circular D-ring decrease the probability of fiber breakage and provide an accurate placement of fiber tows on e mandre The pay-out eye system was set up on a translation tage which provided the translational motion for the Surfactant AgentPS2 fiber tow. The impregnated fibers were then wound around the mandrel over a predefined geodesic path. The PolyMer two couplings which were attached to a bearing at each end, and finally the whole system was connected rotary motor. The translational and rotational motions of the translation stage and rotary motor were con- rolled by a multi-dimensional motion programmable controller(the white box on the table in Fig 3)[31]. The Pyrola filtration program was written in G-code machine language to wind the impregnated fiber tows on the mandrel with t 82 4-degree helical paths. It should be mentioned that a hoop-winding is a 90-degree winding by convention. The translation, rotation, and winding speed were adjusted at 128 mm/min, 8 rpm(958 mm/min), and 966.5 mm/min respectively. The cure-on-the-fly technique was used Fig. 1. CFCC particle filled matrix fabrication methodology during the winding of the impregnated fiber tows around the mandrel drel [ 19, 20]. Two infrared heaters on both sides the mixture of 70 wt. BlackglasTM with 30 wt. of the mandrel kept the temperature of the mandrel and selected powder. The particle-filled preceramic polymer composite substrate around 50-60oC to partially cure with surfactant agent was mixed for 24 h using a mag- the part(see Fig 3) netic stirrer to give a desirable dispersion of powder in The wound shell and mandrel were then placed in a the polymer for the fabrication process. Addition of the pre-heated oven to complete the B-staging. The sample in Hypermer PS2 surfactant agent in the amount equal to this step is at the green stage. The part and mandrel were 5 wt. of the powder mixed in the Blackglas M gave a held for I h at 55C and 2 h at 150 C in a pre-heated desirable dispersion to the Blackglas/filler system[30] oven. The final step was the pyrolysis/reinfiltration cycles The second step was to impregnate the coated fiber by The part was slipped off the mandrel and placed in a passing it through the resin bath that was filled with the high temperature furnace(see Fig. 3)with a nitrogen mixture of particle filled preceramic polymer and sur- environment for the pyrolysis step The pyrolysis tem- factant agent PS2. Fig. 2 shows the schematic of the perature profile for the CfCC with and without an inert
the mixture of 70 wt.% BlackglasTM with 30 wt.% selected powder. The particle-filled preceramic polymer with surfactant agent was mixed for 24 h using a magnetic stirrer to give a desirable dispersion of powder in the polymer for the fabrication process. Addition of the Hypermer PS2 surfactant agent in the amount equal to 5 wt.% of the powder mixed in the BlackglasTM gave a desirable dispersion to the Blackglas/filler system [30]. The second step was to impregnate the coated fiber by passing it through the resin bath that was filled with the mixture of particle filled preceramic polymer and surfactant agent PS2. Fig. 2 shows the schematic of the tensioner assembly and particle filled preceramic polymer resin bath. The tensioner system was adjusted mechanically to apply constant tension of 8.89 N to the Nextel1 fiber tow and 11.15 N to the NicalonTM fiber tow. These values were determined experimentally during the fabrication of CFCCs. In the third step,the impregnated fiber tows were guided through the pay-out eye system which consisted of 8 rollers and a semi-circular D-ring. The use of the rollers and semi-circular D-ring decrease the probability of fiber breakage and provide an accurate placement of fiber tows on the mandrel. The pay-out eye system was set up on a translation stage which provided the translational motion for the fiber tow. The impregnated fibers were then wound around the mandrel over a predefined geodesic path. The mandrel was made of stainless steel and placed between two couplings which were attached to a bearing at each end,and finally the whole system was connected to a rotary motor. The translational and rotational motions of the translation stage and rotary motor were controlled by a multi-dimensional motion programmable controller (the white box on the table in Fig. 3) [31]. The program was written in G-code machine language to wind the impregnated fiber tows on the mandrel with 82.4-degree helical paths. It should be mentioned that a hoop-winding is a 90-degree winding by convention. The translation,rotation,and winding speed were adjusted at 128 mm/min,8 rpm (958 mm/min),and 966.5 mm/min, respectively. The cure-on-the-fly technique was used during the winding of the impregnated fiber tows around the mandrel [19,20]. Two infrared heaters on both sides of the mandrel kept the temperature of the mandrel and composite substrate around 50–60 C to partially cure the part (see Fig. 3). The wound shell and mandrel were then placed in a pre-heated oven to complete the B-staging. The sample in this step is at the green stage. The part and mandrel were held for 1 h at 55 C and 2 h at 150 C in a pre-heated oven. The final step was the pyrolysis/reinfiltration cycles. The part was slipped off the mandrel and placed in a high temperature furnace (see Fig. 3) with a nitrogen environment for the pyrolysis step. The pyrolysis temperature profile for the CFCC with and without an inert Table 3 Specifications of the inert powder inclusions Property Si3N4 SiC TiC TiN Density (g/cm3 ) 3.18 3.2 5.22 4.93 Particle size range (mm) 0.3–1.2 0.25–1.3 0.8–1.2 1.0–1.5 Mean particle size (mm) 0.5 0.6 1 1.2 Melting point (C) 2650 2700 2950 3050 Stability in the air Stable Stable Stable Stable Fig. 1. CFCC particle filled matrix fabrication methodology. Table 2 Physical properties of NicalonTM and Nextel1 312 fibers Property NicalonTM Nextel1 312 Density (g/cm3 ) 2.32 2.70 Coefficient of thermal expansion (106 / C) 4 3 Tensile strength (GPa) 2.93 1.72 Elastic modulus (GPa) 186 138 Strain to failure (%) 1.60 1.20 Filament diameter (mm) 10–12 10–12 Fig. 2. Tensioner assembly and particle filled preceramic polymer resin bath. A. Yousefpour, M.N. Ghasemi Nejhad / Composites Science and Technology 61 (2001) 1813–1820 1815
l816 A. Yousefpour, M.M. Ghasemi Nejad/ Composites Science and Technology 61(2001)1813-1820 Fig 3. Photograph of the filament winding set-up Fig. 4. Nextel fiber-reinforced CFCC tube with Si,N4 inert particle filled blackglas particle filled preceramic started from 150 to 200C at of coated fiber"/ Blackglas-"type of filler". For example, the rate of 2C/min, held at 200C for I h, heated from Nextel/ Blackglas-SiC indicates Nextel/ Blackglas with 200 to 1000C at the rate of 3C/min, then held for 1 h SiC particle filled matrix, and Nextel/ Blackglas-Si3N at 1000C. The temperature was then lowered from indicates Nextel Blackglas with Si3 n4 particle filled 1000 to 250C at the rate of 3C/min. Finally, the matrix, etc. sample reached room temperature under natural con Mechanical performances of the fabricated tubes were vection. The weight and dimensions of the samples were determined using C-ring test C-ring test is known as a recorded throughout the reinfiltration/pyrolysis cycles. reliable technique to measure the flexural strength and The reinfiltration step was necessary to increase the part modulus of tubular ceramic specimens [32]. Six C-ring density and fill the voids and microcracks inside the specimens were cut off the uniform section of the CFCC matrix, and was achieved by submerging the samples in tubes using a diamond saw. Thickness, width, and inner BlackglasTM. The samples were held in the preceramic radius were measured and recorded using a digital polymer for half an hour to soak completely and fill the micrometer, and were found to have average values of voids and microcracks with the polymer. Then, the 1.65, 6.0, and 18.1 mm, respectively. All C-ring tests nfiltrated part was placed in the oven again for B-sta- were performed on an Instron machine at room tem- ging and cross-linking at 55C for I h and 150C for 2 perature. The speed of the moving cross-head was 2 h. The samples were then pyrolyzed using the pyrolysis mm/min. The fracture strength of C-ring specimens can temperature profile, mentioned earlier, to partially con- be calculated by using curve beam theory [33] vert the polymer to ceramic. Again, the weight and dimensions of the parts were measured and recorded The reinfiltration/pyrolysis cycles(5-7 cycles)stopped 4. Results and discussion when the last sequential weight gain of the samples was around 2%. When the weight convergence was achieved The change in weight gain between each pyrolysis/ the density of the composite part was measured. Each reinfiltration cycle was used for the convergence criter- reinfiltration/pyrolysis cycle took about 17 h. It took ion and achieved when it was less that 2%. Table 4 shows about 8 h to wind a tube. A typical manufactured CFCc processing results for each sample. The weight gain per- is shown in Fig. 4. The fiber turn-around, during the centage is compared with the weight of the sample after winding, was achieved by turning around on the cylind- its first pyrolysis. Also, the thickness change percentage, rical surface of the mandrel towards its ends as opposed in Table 4, shows that samples with fillers exhibit excel- to a turn-around over the mandrel end domes. As a lent shape retention and dimensional stability compared result, samples had higher thickness at their ends as seen with those without fillers. A negative thickness change in Fig. 4. These ends were trimmed prior to cutting the denotes shrinkage. Table 5 gives the summary of the tubes to obtain C-ring test samples results obtained from the C-ring test for the samples After initial runs and quality check, optimum proces- Failure displacement, strength, and modulus are given sing parameters were determined. Then, eight con- with their respective standard deviations in parentheses tinuous fiber reinforced ceramic composite tubes with Although the particle size may have an effect on the final average length of 94.82 mm, inner diameter of 38.1 processing and performance of the CFCCs [34),no mm,and thickness of 1.65 mm were manufactured. The parametric study on the particle size effects was per samples were named using the following initials, type formed in the present work
particle filled preceramic started from 150 to 200 C at the rate of 2 C/min,held at 200 C for 1 h,heated from 200 to 1000 C at the rate of 3 C/min,then held for 1 h at 1000 C. The temperature was then lowered from 1000 to 250 C at the rate of 3 C /min. Finally,the sample reached room temperature under natural convection. The weight and dimensions of the samples were recorded throughout the reinfiltration/pyrolysis cycles. The reinfiltration step was necessary to increase the part density and fill the voids and microcracks inside the matrix,and was achieved by submerging the samples in BlackglasTM. The samples were held in the preceramic polymer for half an hour to soak completely and fill the voids and microcracks with the polymer. Then,the infiltrated part was placed in the oven again for B-staging and cross-linking at 55 C for 1 h and 150 C for 2 h. The samples were then pyrolyzed using the pyrolysis temperature profile,mentioned earlier,to partially convert the polymer to ceramic. Again,the weight and dimensions of the parts were measured and recorded. The reinfiltration/pyrolysis cycles (5–7 cycles) stopped when the last sequential weight gain of the samples was around 2%. When the weight convergence was achieved, the density of the composite part was measured. Each reinfiltration/pyrolysis cycle took about 17 h. It took about 8 h to wind a tube. A typical manufactured CFCC is shown in Fig. 4. The fiber turn-around,during the winding,was achieved by turning around on the cylindrical surface of the mandrel towards its ends as opposed to a turn-around over the mandrel end domes. As a result,samples had higher thickness at their ends as seen in Fig. 4. These ends were trimmed prior to cutting the tubes to obtain C-ring test samples. After initial runs and quality check,optimum processing parameters were determined. Then,eight continuous fiber reinforced ceramic composite tubes with final average length of 94.82 mm,inner diameter of 38.1 mm,and thickness of 1.65 mm were manufactured. The samples were named using the following initials,‘‘type of coated fiber’’/Blackglas–‘‘type of filler’’. For example, Nextel/Blackglas–SiC indicates Nextel/Blackglas with SiC particle filled matrix,and Nextel/Blackglas–Si3N4 indicates Nextel/Blackglas with Si3N4 particle filled matrix,etc. Mechanical performances of the fabricated tubes were determined using C-ring test. C-ring test is known as a reliable technique to measure the flexural strength and modulus of tubular ceramic specimens [32]. Six C-ring specimens were cut off the uniform section of the CFCC tubes using a diamond saw. Thickness,width,and inner radius were measured and recorded using a digital micrometer,and were found to have average values of 1.65,6.0,and 18.1 mm,respectively. All C-ring tests were performed on an Instron machine at room temperature. The speed of the moving cross-head was 2 mm/min. The fracture strength of C-ring specimens can be calculated by using curve beam theory [33]. 4. Results and discussion The change in weight gain between each pyrolysis/ reinfiltration cycle was used for the convergence criterion and achieved when it was less that 2%. Table 4 shows processing results for each sample. The weight gain percentage is compared with the weight of the sample after its first pyrolysis. Also,the thickness change percentage, in Table 4,shows that samples with fillers exhibit excellent shape retention and dimensional stability compared with those without fillers. A negative thickness change denotes shrinkage. Table 5 gives the summary of the results obtained from the C-ring test for the samples. Failure displacement,strength,and modulus are given with their respective standard deviations in parentheses. Although the particle size may have an effect on the processing and performance of the CFCCs [34],no parametric study on the particle size effects was performed in the present work. Fig. 4. Nextel1 fiber-reinforced CFCC tube with Si3N4 inert particle filled blackglasTM. Fig. 3. Photograph of the filament winding set-up. 1816 A. Yousefpour, M.N. Ghasemi Nejhad / Composites Science and Technology 61 (2001) 1813–1820
A. Yousefpour, M.M. Ghasemi Nejad/ Composites Science and Technology 61(2001)1813-1820 18 Table 4 Blackglas-TiC, Nextel/ Blackglas-TIN, and Next rocessing results Blackglas. Among all Nextel-based samples with pow- Specimen" Pyrolysis Final density Weight gain Thickness change der inclusion, Nextel/Blackglas-TiN shows the highest (g/cm) strength. The strength of Nextel/ Blackglas-TiN at 20. MPa is slightly lower than that of Nextel/Blackglas at Ne/BG-SiC 5 217 MPa. Using SiC, Si3N4 and TiC powders as powder Ne/BG-Tic 6 inclusions decreased the strength of CFCC parts by about 28% compared with that of Nextel/Blackglas Ne/ BG The strength of Nextel/Blackglas-Tin decreased by only 6% compared with that of Nextel/ Blackglas Fig. 6 Blackglas-Si3N4, Nicalon/ BlackglaS-TIN, and Nicalon, Ne, Nextel; Ni, Nicalon: BG. Blackglas Blackglas samples. It is observed that Nicalon-based samples with powder inclusion exhibited lower strength 4.1. Efects of inert powder inclusion on Nextel and than that of Nicalon/ Blackglas samples. Nicalon/ Black ased CFCC glas-Si3 N4 and Nicalon/ Blackglas-TiN showed 33 and All samples with particle filled matrix required less tively. A lower strength of CFCCs with powder inclu pyrolysis/infiltration cycles to achieve a weight con- sion can be attributed to their possible early closure and vergence(see Table 4). Nextel/ Blackglas and Nicalon/ lower density, considering the fact that the density of all Blackglas required seven pyrolysis/infiltration cycles to inclusions are more than that of the Nextel/ Blackglas achieve a weight convergence. Adding inert particles in and Nicalon/ Blackglas CFCCs(see Tables 3 and 4). It BlackglasTM increased the green density (i.e. the density should also be mentioned that the Nextel/ Blackglas and of the sample before the first pyrolysis) of the part, and Nicalon/ Blackglas CFCCs had slightly higher fiber the weight convergence occurred faster than samples volume fractions compared with their counterparts with with no powder inclusion(see Table 4). The cumulative particle inclusions weight gain of Nextel/ Blackglas and Nicalon/Blackgla Nextel/Blackglas-TiC and Nextel/ Blackglas-SiC exhib- were higher than that of samples with inert powder ited higher stifness compared with Nextel/ Blackglas- inclusion. The possible reasons are that the samples with Si3 N4 and Nextel/ Blackglas-tin(see Table 5). This result could be attributed to the higher stifness of TiC, cracks in their matrix, and the added ceramic particles 460 GPa, and SiC, 420 GPa, compared with that of might have caused an early closure leading to an early Si3N4, 320 GPa, and TIN, 250 GPa. Table 5 also shows weight gain convergence and hence lower final density the displacement to failure for all samples. As it was compared with the Nextel/ Blackglas and Nicalon/ expected, stiffer materials had generally a lower dis Blackglas CFCCs. Samples were cut from various loca- placement to failure. It should also be mentioned that tions of the tubes and their average fiber volume frac- the Nicalon/Blackglas and Nextel/ Blackglas CFCCs tion and porosity content were found to be 63 and 6% had slightly higher fiber volume fractions compared for Nextel-based samples with powder inclusion and 65 with their counterparts with particle inclusions In gen- and 4% for Nextel/ Blackglas samples, respectively, using eral, samples with powder inclusions had lower strength SEM micrographs and planimeter. The Nicalon/Black- and displacement to failure(see Table 5). However, the glas-Si3N4 and Nicalon/ Blackglas-TiN samples had an modulus was either maintained or increased for samples average fiber volume fraction and porosity content of 60 with powder inclusions(see Table 5), which could be and 6%, respectively. Nicalon/ Blackglas samples had an due to the effect of higher moduli for the inclusions average fiber volume fraction and porosity of 62 and compared with the based materials 4%, respectively It should be noted that the winding angle in this work Fig 5 compares the strength results of C-ring test for was 82.4(and not an exact hoop winding, i.e. 90 Nextel/ Blackglas-SiC, Nextel/ Blackglas-Si3 N4, Nextel/ winding), and hence the samples were loaded in an Table 5 C-ring test resultsa Ne/BG-SiC Ne/BG-Sin Ne/BG-TiC Ne/BG-Tin Ne/BG Ni/BG-TIN Ni/BG 1.83(0.06)2.11(0.03)1.77(0.18)2600.56)2.750.10)0.92008)1.18(0.20)1.69(0.10) 677(60.6)163.9(14.9)156.8(19.3)2041(52.3)216.7(15.8)105.0(16.2)117.1(15.6)149.9(8.2) Modulus(GPa) 627(55)50.5(7.3)61.6(4.3)51.7(12.4)50.8(40) 72.5(5.6 654(5.4) 99(12.0) Ne, Nextel: Ni. Nicalon: BG. Blackglas
4.1. Effects of inert powder inclusion on Nextel1 and Nicalon TM based CFCCs All samples with particle filled matrix required less pyrolysis/infiltration cycles to achieve a weight convergence (see Table 4). Nextel/Blackglas and Nicalon/ Blackglas required seven pyrolysis/infiltration cycles to achieve a weight convergence. Adding inert particles in BlackglasTM increased the green density (i.e. the density of the sample before the first pyrolysis) of the part,and the weight convergence occurred faster than samples with no powder inclusion (see Table 4). The cumulative weight gain of Nextel/Blackglas and Nicalon/Blackglas were higher than that of samples with inert powder inclusion. The possible reasons are that the samples with inert powder inclusion had more voids,porosity,or cracks in their matrix,and the added ceramic particles might have caused an early closure leading to an early weight gain convergence and hence lower final density compared with the Nextel/Blackglas and Nicalon/ Blackglas CFCCs. Samples were cut from various locations of the tubes and their average fiber volume fraction and porosity content were found to be 63 and 6% for Nextel-based samples with powder inclusion and 65 and 4% for Nextel/Blackglas samples,respectively,using SEM micrographs and planimeter. The Nicalon/Blackglas–Si3N4 and Nicalon/Blackglas–TiN samples had an average fiber volume fraction and porosity content of 60 and 6%,respectively. Nicalon/Blackglas samples had an average fiber volume fraction and porosity of 62 and 4%,respectively. Fig. 5 compares the strength results of C-ring test for Nextel/Blackglas–SiC,Nextel/Blackglas–Si3N4,Nextel/ Blackglas–TiC,Nextel/Blackglas–TiN,and Nextel/ Blackglas. Among all Nextel-based samples with powder inclusion,Nextel/Blackglas–TiN shows the highest strength. The strength of Nextel/Blackglas–TiN at 204 MPa is slightly lower than that of Nextel/Blackglas at 217 MPa. Using SiC,Si3N4 and TiC powders as powder inclusions decreased the strength of CFCC parts by about 28% compared with that of Nextel/Blackglas. The strength of Nextel/Blackglas–TiN decreased by only 6% compared with that of Nextel/Blackglas. Fig. 6 compares the strength results of C-ring test for Nicalon/ Blackglas–Si3N4,Nicalon/Blackglas–TiN,and Nicalon/ Blackglas samples. It is observed that Nicalon-based samples with powder inclusion exhibited lower strength than that of Nicalon/Blackglas samples. Nicalon/Blackglas–Si3N4 and Nicalon/Blackglas–TiN showed 33 and 22% lower strength than Nicalon/Blackglas,respectively. A lower strength of CFCCs with powder inclusion can be attributed to their possible early closure and lower density,considering the fact that the density of all inclusions are more than that of the Nextel/Blackglas and Nicalon/Blackglas CFCCs (see Tables 3 and 4). It should also be mentioned that the Nextel/Blackglas and Nicalon/Blackglas CFCCs had slightly higher fiber volume fractions compared with their counterparts with particle inclusions. Nextel/Blackglas–TiC and Nextel/Blackglas–SiC exhibited higher stiffness compared with Nextel/Blackglas– Si3N4 and Nextel/Blackglas–TiN (see Table 5). This result could be attributed to the higher stiffness of TiC, 460 GPa,and SiC,420 GPa,compared with that of Si3N4,320 GPa,and TiN,250 GPa. Table 5 also shows the displacement to failure for all samples. As it was expected,stiffer materials had generally a lower displacement to failure. It should also be mentioned that the Nicalon/Blackglas and Nextel/Blackglas CFCCs had slightly higher fiber volume fractions compared with their counterparts with particle inclusions. In general,samples with powder inclusions had lower strength and displacement to failure (see Table 5). However,the modulus was either maintained or increased for samples with powder inclusions (see Table 5),which could be due to the effect of higher moduli for the inclusions compared with the based materials. It should be noted that the winding angle in this work was 82.4 (and not an exact hoop winding,i.e. 90 winding),and hence the samples were loaded in an Table 4 Processing results Specimena Pyrolysis cycles Final density (g/cm3 ) Weight gain (%) Thickness change (%) Ne/BG–SiC 5 2.40 17 0.74 Ne/BG–SiN 5 2.40 16 1.67 Ne/BG–TiC 6 2.41 19 0.86 Ne/BG–TiN 5 2.41 18 0.95 Ne/BG 7 2.47 27 4.27 Ni/BG–SiN 6 2.14 22 0.58 Ni/BG–TiN 5 2.15 22 0.84 Ni/BG 7 2.18 26 2.59 a Ne,Nextel; Ni,Nicalon; BG,Blackglas. Table 5 C-ring test resultsa Flexural properties Ne/BG–SiC Ne/BG–SiN Ne/BG–TiC Ne/BG–TiN Ne/BG Ni/BG–SiN Ni/BG–TiN Ni/BG Displacement (mm) 1.83 (0.06) 2.11 (0.03) 1.77 (0.18) 2.60 (0.56) 2.75 (0.10) 0.92 (0.08) 1.18 (0.20) 1.69 (0.10) Strength (MPa) 167.7 (60.6) 163.9 (14.9) 156.8 (19.3) 204.1 (52.3) 216.7 (15.8) 105.0 (16.2) 117.1 (15.6) 149.9 (8.2) Modulus (GPa) 62.7 (5.5) 50.5 (7.3) 61.6 (4.3) 51.7 (12.4) 50.8 (4.0) 72.5 (5.6) 65.4 (5.4) 59.9 (12.0) a Ne,Nextel; Ni,Nicalon; BG,Blackglas. A. Yousefpour, M.N. Ghasemi Nejhad / Composites Science and Technology 61 (2001) 1813–1820 1817
l818 A. Yousefpour, M.M. Ghasemi Nejad/ Composites Science and Technology 61(2001)1813-1820 22 Ne/BGSiC Ne/BG SiN Ne/BG-TiC Ne/BG-TiN Ne/RG 0,00 NVBG-Sin Ne/BG-Sin NUBG-TiN Ne/RG-TIN NiBc glas-Si3N4, Nextel/ Blackglas-TiC, Nextel/Blackglas-TIN, and Next Blackglas Fig. 7. Displacement to failure comparison of Nicalon/ Blackglas- Si3N4 and Nextel/ Blackglas-Si3N4, Nicalon/ Blackglas-TiN and Nex el/ Blackglas-TiN, and Nicalon/ Blackglas and Nextel/ Blackglas BG- Blackglas 500 200.0 Fig. 6. Strength comparison of Nicalon/Blackglas-Si3N4, Nicalo Blackglas-TIN, and Nicalon/ Blackgla angle-ply configuration in the C-ring tests which will lackglas-Si3 N4 and Nextel, Blackglas-Si3N4, Nicalon/ Blackglas-TiN and Nextel/ Blackglas-TiN reduce the strength and stiffness of samples compared and Nicalon/ Blackglas and Nextel/ blackglas with coupons having their fibers placed in the load direction H Nextel 4.2. Effects of a material system BG- Blackzlas Effects of a material system can be observed by inves- tigating the manufacturing processing and mechanical performances of three groups of samples, i.e.(1)Nica lon/ Blackglas-Si3 N4 and Nextel/ Blackglas-Si3 N4, (2) Nicalon/ Blackglas-TiN and Nextel/Blackglas-TiN and ()Nicalon/ Blackglas and Nextel/ Blackglas. It should be noted that, the matrix material and particle inclusion are the same in the samples for each group, and only the coated fiber reinforcements are different. Although the strength and strain to failure of Nicalon fiber are higher Fig 9. Modulus comparison of Nicalon/Blackglas-SigN4 and Nextel, than those for Nextel fiber(see Table 2), Nextel/Black- Blackglas- si Na, Nicalon/ B in and NexteBlackglas-TiN glas-Si3N4, Nextel/ Blackglas-TiN, and Nextel/ Black glas composite samples exhibited higher displacement to failure and fracture strength compared with Nicalon/ Figs. 7 and 8 and shows a higher modulus for Nicalon- Blackglas-Si3N4, Nicalon/BlackglaS-TiN, and Nicalon/ based samples compared with Nextel-based samples Blackglas composite samples(see Table 5 and Figs. 7 This result was expected because of higher modulus of and 8). This could in part be attributed to a better inter- Nicalon fiber compared with that of Nextel fiber(see face performance of BN-coating, for Nextel fiber, over C- Table 2) coating, for Nicalon fiber(see the Introduction section for It was observed that BN-Nextel-based samples the effects of interface). Fig. 9 is the counterpart for bited somewhat more fiber pull-out compared
angle-ply configuration in the C-ring tests which will reduce the strength and stiffness of samples compared with coupons having their fibers placed in the load direction. 4.2. Effects of a material system Effects of a material system can be observed by investigating the manufacturing processing and mechanical performances of three groups of samples,i.e. (1) Nicalon/Blackglas–Si3N4 and Nextel/Blackglas–Si3N4,(2) Nicalon/Blackglas–TiN and Nextel/Blackglas–TiN and (3) Nicalon/Blackglas and Nextel/Blackglas. It should be noted that,the matrix material and particle inclusion are the same in the samples for each group,and only the coated fiber reinforcements are different. Although the strength and strain to failure of Nicalon fiber are higher than those for Nextel fiber (see Table 2),Nextel/Blackglas–Si3N4,Nextel/Blackglas–TiN,and Nextel/Blackglas composite samples exhibited higher displacement to failure and fracture strength compared with Nicalon/ Blackglas–Si3N4,Nicalon/Blackglas–TiN,and Nicalon/ Blackglas composite samples (see Table 5 and Figs. 7 and 8). This could in part be attributed to a better interface performance of BN-coating,for Nextel fiber,over Ccoating,for Nicalon fiber (see the Introduction section for the effects of interface). Fig. 9 is the counterpart for Figs. 7 and 8 and shows a higher modulus for Nicalonbased samples compared with Nextel-based samples. This result was expected because of higher modulus of Nicalon fiber compared with that of Nextel fiber (see Table 2). It was observed that BN-Nextel-based samples exhibited somewhat more fiber pull-out compared with Fig. 5. Strength comparison of Nextel/Blackglas–SiC,Nextel/Blackglas–Si3N4,Nextel/Blackglas–TiC,Nextel/Blackglas–TiN,and Nextel/ Blackglas. Fig. 7. Displacement to failure comparison of Nicalon/Blackglas– Si3N4 and Nextel/Blackglas–Si3N4,Nicalon/Blackglas–TiN and Nextel/Blackglas–TiN,and Nicalon/ Blackglas and Nextel/Blackglas. Fig. 6. Strength comparison of Nicalon/Blackglas–Si3N4,Nicalon/ Blackglas–TiN,and Nicalon/Blackglas. Fig. 8. Strength comparison of Nicalon/Blackglas–Si3N4 and Nextel/ Blackglas–Si3N4,Nicalon/Blackglas–TiN and Nextel/Blackglas–TiN, and Nicalon/Blackglas and Nextel/Blackglas. Fig. 9. Modulus comparison of Nicalon/Blackglas–Si3N4 and Nextel/ Blackglas–Si3N4,Nicalon/Blackglas–TiN and Nextel/Blackglas–TiN, and Nicalon/Blackglas and Nextel/ Blackglas. 1818 A. Yousefpour, M.N. Ghasemi Nejhad / Composites Science and Technology 61 (2001) 1813–1820
A. Yousefpour, M.M. Ghasemi Nejad/ Composites Science and Technology 61(2001)1813-1820 C-Nicalon-based ones. Table 5 reveals that samples Curtin WA. Theory of mechanical properties of ceramic-matrix omposed of BN-Nextel are 30-45% stronger than composites. J Am Ceram Soc 1991: 74/11: 2837-45. those composed of C-Nicalon. In general, samples (5 Wang Sw, Parvizi-Majidi A Mechanical behavior of Nicalon composed of BN- Nextel fiber reinforcement showed better mechanical performance than those composed of Ceram Eng Sci Proc 1990: 11/9-10: 1607-16 [6 Singh RN. Fiber-matrix interfacial characteristics in a fiber-rein- C- Nicalon fiber reinforcement This trend could be due forced ceramic-matrix composite. J Am Ceram Soc 1989: 72/9 to a better performance of BN-coating over C-coating in the processes employed in this work. No detailed [7 Keith WP, Kedward KT. Shear damage mechanism in a woven, studies were performed to determine any possible coat icalon reinforced ceramic matrix composite. J Am Ceram Soc ing damage during the filament winding process which [8] Jacobson NS, Morscher GN, Bryant DR, Tressler RE. High is a subject of the future studies mperature oxidation of boron nitride: Il, boron nitride layers mposites. J Am Ceram Soc 1999: 82/6: 1473-82. 9 Kernas RJ, Hay RS, Pagano NJ, Parthasarathy TA. The role of 5. Conclusions ne fiber-matrix interface in ceramic composites. Am Ceram Soc Bull198968/2:4294 [0] Evans AG, Marshall DB. The mechanical behavior of ceramic Filament winding using preceramic polymer pyrolysis matrix composite. Acta Metall 1989: 37/10.2567-83 is a versatile method to manufacture Continuous fiber [1] Kernas RJ, Rebillat F, Lamon J Fiber-matrix interface proper- Ceramic Composites (CFCCs) with a BlackglasTM ties of single-fiber microcomposites as matrix. It is found that the inert powder inclusion redu tests. J Am Ceram Soc 1997: 80/2: 506-8 [12 Courtney TH. Mechanical behavior of materials. New York: ces the time of production of CFCCs by 14-28% and McGraw-Hill. 1990. also obtains excellent shape retention. It is believed that [13] Evans AG, He MY Interface debonding and fiber cracking in the inclusion of inert powders causes premature closure brittle matrix composites. J Am Ceram Soc 1989: 72/12: 2300- of the samples during reinfiltration/pyrolysis process, which lead to a faster weight convergence but a lower [14 Charalambides PG, Evans AG. Debonding properties of residu- ally stressed brittle-matrix composites. J Am Ceram Soc 1989 density and higher porosity, compared with the baseline parts (i.e, samples with no powder inclusion). The [15] Sun EY, Nutt SR, Brennan JJ. Fiber coating for SiC-fiber-rein strength and displacement to failure dropped by 6-28% rced BMAs glass-ceramic composites. J Am Ceram Soc 1997; and 5-33%, respectively for Nextel-based samples, and 8/1:2646. the same values for Nicalon-based samples were 22- [16] Naslain R, Dugne O, Gutte A, Sevely J, Brosse CR, Rocher JP, Cotteret J Boron Nitride Interphase in Ceramic-Matrix Compo- 33% and 30-46%, respectively. Investigation on the sites. J Am Ceram Soc 1991: 74/10: 2482-8 effects of fiber and fiber coating material systems used [17] Lu MC. Evaluation of interfacial properties in ceramic coating/ here showed that BN-Nextel fiber reinforced samples mposites. Ceram Eng Sci Proc 1990: 11/ 9-10 had better mechanical performance than their C-Nica- (8 Soden PD, Kitvhing R, Tse PC. Tsavalas y Influence of winding lon"M counterparts, even though Nicalon fiber is ngle on the strength and deformation of filament-wound com- subjected to uniaxial loads Composites Science and stronger than Nextel 312 fiber. This was attributed to echnology1992:46:363-78 better fiber/matrix interphase performance provided [19] Chandramouli, M. V, Manufacturing of near-net shape ceramic by BN-coating matrix composites by filament winding and preceramic polymer pyrolysis. Master thesis. Department of Mechanical Engineering, University of Hawaii at Manoa, 1995. 20 Ghasemi Nejhad MN, MV. Wereszczak AA. Acknowledgements Processing and performance of Sic/Blackglas CFCCs using fila- lent winding. Ceram Eng Sci Proc 1996: 17/4: 449-58 The authors are thankful to the AlliedSignal, Inc (Ho- [21] Semen J, Loop JG. A preceramic polymer route to model Sic ceramic parts. Ceram Eng Sci Proc 1990: 12/9: 1967-80 keywell), for the BlackglasTM donation and BN coating [22] Mallick PK Fiber-reinforced composite: materials, manufactur. of the Nextel 312 fibers. We also thank 3M company for the donation of the nextel r 312 fibers. C-Nicalon ing, and design. New York: Marcel Dekker, 1993. 23] Hu C, Parvizi-Majidi A. Investigation of sol-gel processing of was purchased from Dow Corning Corporation. ceramic matrix composites. AMD-Vol 194, Mechanics in Mat rials Processing and Manufacturing 1994: 353--60 [24] Allied-Signal Inc. Blackglas M Technology, 1997 References [25]3M, Properties of Nextel 312 and 440 ceramic fibers, technical data. 1997. [1 Park K, Dipietro SG, Thurston GS. Microstructural studies of 6] Dow Corning Corporation. Information about Nicalon cera- Sic continuous fiber/nitrided-bonded SiC composites. J Mater 27 ICI Americas Inc Operation and technical manual, 1994 [2 Cutler WA, Zok FW, Lange FF. Mechanical behavior of several [28] UBE Industries Ltd. Information about silicon nitride powder hybrid ceramic-matrix-composite laminates. J Am Ceram Soc 1997. 1996:79/7:1825-3 [29] H C Starck Inc. Information about silicon nitride powder, 1997 3 Riccitiello S, Marshall MK. 3-D ceramic matrix composi 0 Bergstrom L Colloidal processing of a very fine BaTi3 powder development. Journal of Advanced Materials 1994: 25/2: 22-8. effect of particle interactions on the suspension properties
C-Nicalon-based ones. Table 5 reveals that samples composed of BN-Nextel are 30–45% stronger than those composed of C-Nicalon. In general,samples composed of BN-Nextel fiber reinforcement showed better mechanical performance than those composed of C-Nicalon fiber reinforcement. This trend could be due to a better performance of BN-coating over C-coating in the processes employed in this work. No detailed studies were performed to determine any possible coating damage during the filament winding process which is a subject of the future studies. 5. Conclusions Filament winding using preceramic polymer pyrolysis is a versatile method to manufacture Continuous Fiber Ceramic Composites (CFCCs) with a BlackglasTM matrix. It is found that the inert powder inclusion reduces the time of production of CFCCs by 14–28% and also obtains excellent shape retention. It is believed that the inclusion of inert powders causes premature closure of the samples during reinfiltration/pyrolysis process, which lead to a faster weight convergence but a lower density and higher porosity,compared with the baseline parts (i.e.,samples with no powder inclusion). The strength and displacement to failure dropped by 6–28% and 5–33%,respectively for Nextel-based samples,and the same values for Nicalon-based samples were 22– 33% and 30–46%,respectively. Investigation on the effects of fiber and fiber coating material systems used here showed that BN-Nextel1 fiber reinforced samples had better mechanical performance than their C-NicalonTM counterparts,even though NicalonTM fiber is stronger than Nextel1 312 fiber. This was attributed to a better fiber/matrix interphase performance provided by BN-coating. Acknowledgements The authors are thankful to the AlliedSignal,Inc.(Honeywell),for the BlackglasTM donation and BN coating of the Nextel1 312 fibers. 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