Characterization and control of the fiber-matrix interface in ceramic ...

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164 ORNL-DWG 88-747iR -10 -12 -4 4 < c. -i6 cu € &? -18 0 m 0 - -20 - 22 - 24 - 26 - 28 5.4 5.8 6.2 6.6 7.0 7.4 7.8 8.2 8.6 i/T (!0-4 K-') Figure 11.5. The diffusion coefficient for selected elements in relative materials.
165 In four of the samples, the fibers were exposed to a silicon-rich environment. These samples exhibited the highest bonds, and fiber tows coated using similar conditions failed before they could be tested. Silicon can diffuse relatively quickly through the silica and react with free carbon to form Sic. If carbon is present as a thin coating around the Sic crystallite, the reaction will accelerate grain growth in the fibers. The Nicalon fibers depend on their amorphous nature for strength, and it has been shown that crystallization and grain growth lead to reductions in fiber strength. The grain growth will also lead to a reduction of grain-boundary volume, forcing the silica to move outward toward the surface of the fibers. This is useful in explaining the high oxygen content a% the fiber-matrix boundary in these samples. The silica layer would strongly bond the fibers to the matrix. These observations contradict the results of the analysis of composites composed of Nicalon fibers in glass or glass-ceramic matrices. Kesearchers have shown that a carbon layer forms at the surface of the fibers when they are hot pressed into an aluminosilicate-based matrix (106-108,150,151). The carbon layer allows for fiber debonding and slip, and the samples exhibit high strength and toughness. Samples without the carbon-rich surface fail in a brittle manner. It has been hypothesized that the carbon diffuses to the surface as CO gas, which reacts with the glass, which is most likely in a reduced state, to produce carbon. An exact explanation for the formation of this layer is unknown. The observed phenomena in the CVI composites may be useful in explaining the events that proceed in the glass-matrix composites. The
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ORNL/TM-11039 Metals and Ceramics D
Page 6 and 7:
Page 9.3 Composite Fabrication . .
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LIST OF TABLES Table Page 5,l. Prop
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Figure 8.3. 9.1.. 9.2. 9.3. 9.4. 9.
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Figure 10.18. 10.19. 10.20. 10. 21.
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ACKNOWLEDGMENTS The author wishes t
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CWCTERIZATION AND CONTROL OF THE FI
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1. INTRODUCTION During the last sev
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The development of low-density, hig
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3. FABRICATION TECHNIQUES 3.1 Intro
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11 isostatic pressing (HIP), can be
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13 utilizing the comparatively low-
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16 ORN L- DWG 85- 4 i 4 18RS HEAT1
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5. COMPOSITE DESIGN 5.1 Introductio
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21 5,2 Mechanical Considerations Th
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23 GRNL-DWG 88-74 26 Figure 5.1. Th
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25 Equation (6) shows that the stre
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27 of reinforcement. There are two
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29 in strength. Conversely, the fib
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-I_- Table 5.2. Thermally induced a
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33 1.2 ID 0.8 ;.r 1 e fi v 0.6 a4 Q
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35 will affect the interface and, t
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38 fiber-matrix bonding; thus, a fu
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40 In the analysis of the mechanica
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42 1.2 I .o .6 - E f aa '3 0.6 cn 3
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44 will result in the matrix being
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I I MATRIX MATRIX Figure 7.1. Schem
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48 F = 2a2H, where H is the hardnes
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50 OWL-PHOTO 6866-86 i d c I 20pm F
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52 where Af is the surface area of
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54 Figure 7.4. Tensile and shear st
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56 I I I / -c rc -c / . Om / / I /
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58 ORNL-OWG 87-i 8234 F Figure 7.7.
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coating and the distribution of she
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62 O m PHOTO 6676-87 i SIC FIBERS -
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the composite, therefore an interme
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methane as the reactant and is, thu
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9. EXPERIMENTAL PROCEDURES 9.1 Depo
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71 furnace. The furnace is, therefo
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73 further protection. A 6.5-cm-dia
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76 of the specimen slowly decreased
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78 The programmer is also equipped
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80 graphite holders through multipl
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82 temperature by simply switching
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84 ORNk DWG 87- 4494 3 METAL LOGR A
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86 9.5 Fracture Surface Analvsis Th
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88 treated and untreated halves wer
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90 9.8.2 Tensile testinq In an init
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92 ORNL-DUG 85-11767R.2 ? ! 2 f CEN
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94 fracture of individual Nicalon f
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96 Figure 10.1. SiC-infiltrated Nic
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99 compared with the dimensions acq
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101 Table 10.3. Strength and modulu
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100 ORNL- DWG 87-1 6292 R CVI-I73 7
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BULK FIBER SAMPLE NO. 173: FIBER SU
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107 similar samples show the film o
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Figure 10.7. SEM micrographs showin
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111 Table 10.4. Thermochemical eval
Page 131 and 132: 100 ORNL-DUG 87-15969R CVI- 170 75
Page 133 and 134: 115 Analysis conversion of of the m
Page 135 and 136: 117 A 1 I S N 31 N I I'd I LN 3H 3
Page 137 and 138: 119 n 0 W n 9 v P n w- n v
Page 139 and 140: 121 s m f c I m z - Ir 2 a 0 9 In u
Page 141 and 142: Figure 10.14. SEM micrographs of in
Page 143 and 144: J ORNL-DWC 88-6289 z cF u) w I- z O
Page 145 and 146: 127 300 I CVI-480 I I 1 0 R N L-DWG
Page 147 and 148: io0 I I I I CVI- 172 75 - - 0 z v -
Page 149 and 150: 131 RAL 033021 RAL 033023 Figure 10
Page 151: 133 include: the reaction of boron
Page 154 and 155: 136 that BN coatings react with the
Page 156 and 157: 75 7 ORNL-DWG 87-48234 50 - - c5 z
Page 158 and 159: 140 Table 10.9. Thermochemical eval
Page 160 and 161: OANL-bwo 88-9025 ORNL-DWG 66-9027 I
Page 162 and 163: 144 uncoated tows were 14 k 2 pm; t
Page 165 and 166: 11. DISCUSSION 11.1 Constituent Pro
Page 167 and 168: 149 The properties of CVD Sic have
Page 169 and 170: 151 11.2.1 Matrix cracking In the N
Page 171 and 172: 153 OWL-DWG 88-10677 CVI- (78 22 I
Page 173 and 174: 155 Table 11.3. Property comparison
Page 175 and 176: 157 a f ““f f- L c I Figure 11.
Page 177 and 178: 159
Page 179 and 180: 161 The equations demonstrate that
Page 181: 163 calculations of the matrix depo
Page 185 and 186: 167 Table 11.4. Properties of glass
Page 187 and 188: 169 rare-earth magnets and coils to
Page 189 and 190: 171 stress fields along the fiber i
Page 191 and 192: 173 11.3.2 Tensile testinp, The use
Page 193 and 194: 17 5 contraction have been ignored,
Page 195: 177 the system, and when the result
Page 198 and 199: 180 reduces fiber strength. The str
Page 200 and 201: 182 15. R. A. J. Sambell, D. H. Bow
Page 202 and 203: 184 41. A. J. Caputo et al., "Fiber
Page 204 and 205: 186 71, N. F. DOW, Study of Stresse
Page 206 and 207: 188 98. M. H. Rawlins et al., "Inte
Page 208 and 209: 190 125. R. Warren and C-H. Anderss
Page 210 and 211: 192 155. M. F. Doerner and W, D. Ni
Page 213 and 214: APPENDIX A. AUGER ELECTRON SPECTROS
Page 215: APPENDIX B DETAILS OF THE FIBER-SHE
Page 218 and 219: 200 Those for the fiber (primed) ar
Page 220 and 221: 202 89-92. 93. 94. 95" 96. 97. 98-9
Page 222 and 223: 204 130-133. E. I. DUPONT DE NEMOUR
Page 224 and 225: 206 173. NATIONAL ACADEMY OF SCIENC
Page 226 and 227: 208 203 - 204. 20s. 206 - 207. 208.
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