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

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110 steps demonstrates that silicon present in the gas phase during the fiber-coating process could react with the excess carbon in the fiber to form silicon carbide (Table 10.4). The reaction disturbs the chemistry and morphology of the fiber, which results in mechanical property degradation. 10.4.2 Elemental silicon The presence of the 0.17-pm silicon coating was verified using X-ray line scan data obtained using a JEOL 733 electron microprobe (Figure 10.8). The flexure specimens exhibited extremely low strength and brittle fracture and no evidence of fiber pull-out or reinforcement. This behavior is displayed in the fracture surfaces and in the loaddisplacement curve in Figure 10.9. Indentation measurements demonstrated that the silicon layer produced extremely high interfacial bonding in the sample. A load of 3 N was required to displace the fibers, and in most tests, the loads heavily damaged the fiber and the surrounding matrix. Extensive cracking of the matrix and crushing of the fibers suggests that the interfacial stresses were approaching the useful limits of the indentation method (Figure 10.10). As with the previous specimens, thermochemical examination of the system suggests the silicon can diffuse into the fiber during interlayer deposition or during further processing. The silicon can react with the free carbon to form Sic, which can damage the integrity of the reinforcement. Tensile testing to determine the strength of the siliconcoated fiber tows was impossible because the specimens failed during heat treatment.
111 Table 10.4. Thermochemical evaluation of the system containing uncoated and Sic-coated fibers. Uncoated fibers 1. S IC + Si02 + C + CH3SiC13 + lOH2 - 1473K 10QKPa 2 SIC + 0.9 SI% + 0.8 C + 18.1 H2 + 2.8 HC1 + 0.2 CO 1473K 2. Si02 + CH3SiC13 + 10H2 __1_3 0.9 Si02 + 0.9 SIC + 1OOKPa 10.2 H2 + 2.6 HC1 +'01 CO -k 0.1 sic1, Nicalon fibers in an HC1 containing environment: Sic + Si02 + C + HC1 - 1473K lOOKPa 0.8 SIC + Si02 + 0.2 C + 0.4 €IC1 + 0.3 H2 + 0.1 SiC1, Silicon carbide from methylsilanea 975K 1. Sic + Si02 + C + SiH4 + CH4- 2 SIC + Si02 + 0.98 C + SIC + Si02 + C + SiH4 + CH4 - 2. Si02 + Sic - 1473K lOOKPa 3. Si02 + SiH4 + CH4 - Si02 + SIC 1125K 3.3KPa 3.3KPa 1125K 3.3KPa Si02 + SIC + 4 H 3.96 H2 + 0.02 CH4 2 SIC + Si02 + C + 4 H2 aNo thermodynamic data were available for CH3SiH3; thus, an analogous system containing SiH4 and CH4 was considered.
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ORNL/TM-11039 Metals and Ceramics D
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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.
Page 78 and 79: coating and the distribution of she
Page 80 and 81: 62 O m PHOTO 6676-87 i SIC FIBERS -
Page 83 and 84: the composite, therefore an interme
Page 85 and 86: methane as the reactant and is, thu
Page 87 and 88: 9. EXPERIMENTAL PROCEDURES 9.1 Depo
Page 89 and 90: 71 furnace. The furnace is, therefo
Page 91 and 92: 73 further protection. A 6.5-cm-dia
Page 94 and 95: 76 of the specimen slowly decreased
Page 96 and 97: 78 The programmer is also equipped
Page 98 and 99: 80 graphite holders through multipl
Page 100 and 101: 82 temperature by simply switching
Page 102 and 103: 84 ORNk DWG 87- 4494 3 METAL LOGR A
Page 104 and 105: 86 9.5 Fracture Surface Analvsis Th
Page 106 and 107: 88 treated and untreated halves wer
Page 108 and 109: 90 9.8.2 Tensile testinq In an init
Page 110 and 111: 92 ORNL-DUG 85-11767R.2 ? ! 2 f CEN
Page 112 and 113: 94 fracture of individual Nicalon f
Page 114: 96 Figure 10.1. SiC-infiltrated Nic
Page 117 and 118: 99 compared with the dimensions acq
Page 119 and 120: 101 Table 10.3. Strength and modulu
Page 121 and 122: 100 ORNL- DWG 87-1 6292 R CVI-I73 7
Page 123 and 124: BULK FIBER SAMPLE NO. 173: FIBER SU
Page 125 and 126: 107 similar samples show the film o
Page 127: Figure 10.7. SEM micrographs showin
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.
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161 The equations demonstrate that
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163 calculations of the matrix depo
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165 In four of the samples, the fib
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167 Table 11.4. Properties of glass
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169 rare-earth magnets and coils to
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171 stress fields along the fiber i
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173 11.3.2 Tensile testinp, The use
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17 5 contraction have been ignored,
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177 the system, and when the result
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180 reduces fiber strength. The str
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182 15. R. A. J. Sambell, D. H. Bow
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184 41. A. J. Caputo et al., "Fiber
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186 71, N. F. DOW, Study of Stresse
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188 98. M. H. Rawlins et al., "Inte
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190 125. R. Warren and C-H. Anderss
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192 155. M. F. Doerner and W, D. Ni
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APPENDIX A. AUGER ELECTRON SPECTROS
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APPENDIX B DETAILS OF THE FIBER-SHE
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200 Those for the fiber (primed) ar
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202 89-92. 93. 94. 95" 96. 97. 98-9
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204 130-133. E. I. DUPONT DE NEMOUR
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206 173. NATIONAL ACADEMY OF SCIENC
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208 203 - 204. 20s. 206 - 207. 208.
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