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2 µm - eTheses Repository - University of Birmingham

2 µm - eTheses Repository - University of Birmingham

1. INTRODUCTION To make

1. INTRODUCTION To make a lightweight material possessing high strength even at higher temperatures, it would be desirable to take advantage of the high strength of low density ceramic materials. Ceramics exhibit brittle behaviour, lacking the required fracture toughness for most heavy duty applications. In contrast, low density metallic materials such as aluminium and magnesium and their alloys, which possess the desired fracture toughness, show low strength at temperatures above 250°C. Thus, for such applications, a composite material combining the desirable properties of two different phases might be vastly superior. The main problem is to effect the combination in such a manner as to exploit the desirable features of both components and thereby maximize the material properties. Aluminium alloys are quite attractive due to their low density, their capability to be strengthened by precipitation, their good corrosion resistance, high thermal and electrical conductivity, and their high damping capacity. The combination of an aluminium alloy and a ceramic material gives a group of materials known as aluminium matrix composites and these have been widely studied since the 1920s (1) and now are used in sporting goods, electronic packaging and automotive industries. They offer a large variety of mechanical properties depending on the chemical composition of the matrix alloy and the reinforcing phase which is predominantly alumina or silicon carbide but MgO, TiO2, SiO2 and CaO may also be considered. The aluminium matrices are in general Al-Si, Al-Cu or Al-Mg alloys. In the 1980s, the transportation industries began to develop discontinuously-reinforced aluminium matrix composites. These aluminium alloy matrices with dispersed ceramic particles are very attractive due to their isotropic room temperature mechanical properties. They are low cost due to cheap processing routes and low cost discontinuous reinforcements. Due to the solely three dimensional connectivity of the metal phase, the main drawbacks of 1

these materials are the detrimental properties regarding creep and mechanical properties at temperatures above 250°C. In recent years, there has been interest in metal matrix composites with interpenetrating networks (2) . Using the Newnham taxonomy (3) , which is based on phase connectivity, such materials are designated 3-3 composites since both phases have connectivity in three dimensions. The combination of materials means not only choosing component phases with the right properties, but also coupling them in the best manner. Connectivity is a key feature in property development in multiphase solids, since physical properties can change by many orders of magnitude depending on the manner in which connections are made. The infiltration of a porous ceramic body, called the preform, with a liquid metal represents an attractive route to fabricate interpenetrated composite materials. The preform route offers a wide variety of types, morphologies and metal volume contents. Thus tailored microstructures with interpenetrated networks can be realised. The properties of the porous ceramics, the metal melt and their interactions are most important regarding the resulting material properties. Furthermore, the local reinforcement of cast metal components is possible. However, industrial applications are often limited mainly by lack of precise knowledge of the influencing factors. Concerning the metal volume fraction, there two forms which have been well studied. One with less than 0.50 and one with more than 0.70. For the higher content chopped fibre and foam-based ceramic materials are used and for metal-reinforced ceramics not more than 0.50 of the metallic phase is used in order to maintain a predominant ceramic behaviour of the resulting materials. The range between 0.50 and 0.70 has not been widely investigated up to date. This is mainly due to the lack of commercially available preforms. 2

  • Page 1 and 2: Pressure Infiltration Behaviour and
  • Page 3 and 4: ABSTRACT In the pressure infiltrati
  • Page 5 and 6: CONTENTS 1. INTRODUCTION 1 2. LITER
  • Page 7 and 8: 4.8.3 Evaluation of infiltration be
  • Page 9 and 10: Symbol Meaning γRv surface energy
  • Page 11: Symbol Meaning TYS tensile yield st
  • Page 15 and 16: 2. LITERATURE REVIEW 2.1. Materials
  • Page 17 and 18: changes in the oxide film chemistry
  • Page 19 and 20: or inside the bulk fluid only. Inte
  • Page 21 and 22: that are most effective in decreasi
  • Page 23 and 24: initiation stress of 25 %. Further,
  • Page 25 and 26: Beffort (36) suggested that even th
  • Page 27 and 28: einforcement interface and reinforc
  • Page 29 and 30: It is interesting to note that, for
  • Page 31 and 32: 20 Table 2.1 Compilation of the mec
  • Page 33 and 34: General models to predict fracture
  • Page 35 and 36: with values observed by others for
  • Page 37 and 38: The work of adhesion characterises
  • Page 39 and 40: and vapour, is difficult to evaluat
  • Page 41 and 42: system Al-Al2O3 is 10 -49 Pa at 700
  • Page 43 and 44: In the Al-Cu system, although the p
  • Page 45 and 46: The heat of reaction ΔGr may be es
  • Page 47 and 48: al. (100) who found non-wetting beh
  • Page 49 and 50: capillary or threshold pressure has
  • Page 51 and 52: using constant gas pressure. Infilt
  • Page 53 and 54: The superficial velocity v0 in the
  • Page 55 and 56: The permeability K can be expressed
  • Page 57 and 58: 2.4. Preform fabrication Composites
  • Page 59 and 60: According to Kniewallner (51) even
  • Page 61 and 62: 2.4.3. Foamed preforms Another inte
  • Page 63 and 64:

    structure. This is shown schematica

  • Page 65 and 66:

    2.5.1. Gas pressure infiltration (G

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    MMCs infiltrated with an Al-9Mg or

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    layer oxide films. The Weber number

  • Page 71 and 72:

    Long et al. (50) suggested that v0

  • Page 73 and 74:

    3. EXPERIMENTAL PROCEDURE The influ

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    sintered at 1550°C, which represen

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    using a AVT-Horn (Aalen, Germany) m

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    squares fit function within the MAP

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    areas, SsBET ,of the powders were m

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    with dimensions of 65 mm x 46 mm x

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    The preform sintering process was o

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    in the evaporation of mercury at lo

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    The compressive strength, σc , of

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    as the measured mean value 0.23. Th

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    for 90 s to ensure complete solidif

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    ottom punch surface. The temperatur

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    A graphic presentation of the relat

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    detected. This operation took appro

  • Page 101 and 102:

    modulus Edyn of the unreinforced al

  • Page 103 and 104:

    calculated using the methods outlin

  • Page 105 and 106:

    Positive volume changes were predic

  • Page 107 and 108:

    Figure 4.5 Droplet formation of the

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    with the metal alloy IM: examples a

  • Page 111 and 112:

    As shown in Figure 4.9, apart from

  • Page 113 and 114:

    4.3.2 Powder specific surface area

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    The particles of TO and MO were dis

  • Page 117 and 118:

    oom temperature and 270°C, with a

  • Page 119 and 120:

    obtain usable products when they we

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    strengths, whereas with 10 and 20 w

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    strength showed no significant diff

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    Relative change in dimension s x, s

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    (a) AOPC20 (b) AGPC15 2 µm (c) TOP

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    At higher magnification, Figure 4.2

  • Page 131 and 132:

    intrusions started at 4 µm and end

  • Page 133 and 134:

    As shown in Figure 4.27, the pore s

  • Page 135 and 136:

    An overview of the specific values

  • Page 137 and 138:

    1.71 to 1.98·10 6 m²/m³. The sim

  • Page 139 and 140:

    logarithmic compression behaviour,

  • Page 141 and 142:

    The volumetric stiffness Eiso of th

  • Page 143 and 144:

    Figure 4.37 shows that the TOPC20 p

  • Page 145 and 146:

    unhindered through the gap between

  • Page 147 and 148:

    intrusions and the other areas were

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    4.8.1 Unreinforced matrix propertie

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    die, Tmelt,die , could not be recor

  • Page 153 and 154:

    pressure was recorded as a function

  • Page 155 and 156:

    the linear fits for AOPC20, TOPC20

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    4.8.6 Non destructive testing of MM

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    X-Y Y-Z Figure 4.51 Virtual cross-s

  • Page 161 and 162:

    The metal filling the intragranular

  • Page 163 and 164:

    the ceramic particles was not visib

  • Page 165 and 166:

    etween the dark grey ceramic phases

  • Page 167 and 168:

    The windows, one of which is marked

  • Page 169 and 170:

    potential interfacial reactions, th

  • Page 171 and 172:

    In order to determine the effect of

  • Page 173 and 174:

    Infiltration depth L² L² (mm²) /

  • Page 175 and 176:

    4.8.12 Microstructure of MMCs with

  • Page 177 and 178:

    minor fraction of suboxides with hi

  • Page 179 and 180:

    4.9. High pressure die casting infi

  • Page 181 and 182:

    In the Y-Z plane section in Figure

  • Page 183 and 184:

    4.9.2 Compression of preforms The c

  • Page 185 and 186:

    Relative preform compression c pr (

  • Page 187 and 188:

    decrease depended on the tooling us

  • Page 189 and 190:

    Bending stress σ (MPa) / MPa 500 4

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    4.10.3 Influence of reinforcement t

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    Significant deformation developed i

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    a) b) 2 50 2 50 µm µm 2 50 2 50

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    5. DISCUSSION First the properties

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    The measured elastic modulus, Edyn

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    The MMCs showed similar wear with t

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    interfacial debonding: Peng et al.

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    The area Sml was derived using data

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    MMC. Due to the solidification shri

  • Page 209 and 210:

    measurements which resulted in a lo

  • Page 211 and 212:

    5.1.5 Influence of reactions No rea

  • Page 213 and 214:

    5.2. Preform pore formation The tar

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    kinetics were reported to be rather

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    The newly formed water vapour led t

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    In order to achieve minimum porosit

  • Page 221 and 222:

    the present work. These pressures w

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    indicated by zero values of the fre

  • Page 225 and 226:

    influence on the pO2,calc. The lowe

  • Page 227 and 228:

    during extended holding and acts as

  • Page 229 and 230:

    Compared to Hg, the Al melt may con

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    preforms with IM, Figure 4.67. For

  • Page 233 and 234:

    preform compression, cpr , increase

  • Page 235 and 236:

    Specific Specific permeability Perm

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    Permeability (m²) / m² 1x10 -12 1

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    As the predominant fluid flow was a

  • Page 241 and 242:

    In the CP mode, the Preform 1D code

  • Page 243 and 244:

    Local Saturation saturation S () lo

  • Page 245 and 246:

    listed in Table 5.1 and 5.3 were us

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    6. CONCLUSIONS 1. An aqueous proces

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    anged between 112 and 131° for the

  • Page 251 and 252:

    8. REFERENCES 1. Altenpohl, D.: Alu

  • Page 253 and 254:

    43. Davis, L.C. and Allison, J.E. :

  • Page 255 and 256:

    85. Gennes, P.G. : “Wetting: Stat

  • Page 257 and 258:

    127. Corbin, S.F., Lee, J. and Qiao

  • Page 259:

    171. Gmelin, L. : Handbook of Inorg

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