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fraction of coarse pores. The alteration of the sintering temperature from 1100°C for TOPC20 to 1050°C for TOPC10 resulted in smaller intragranular pores in the latter. Relative Relative pore pore volume volume () 0.3 0.2 0.1 0.0 10 -1 10 0 Pore diameter (µm) /µm 121 TOPC20 TOPC10 Figure 4.28 Incremental pore size distribution of TOPC10 and TOPC20. The composition and geometry of the pore former influenced the pore size distribution. The carbon fibre pore formation in AOPF20 led to a distinct peak at a diameter of about 8 µm as shown in Figure 4.29 which represents exactly the carbon fibre diameter. Relative pore pore volume volume () 0.3 0.2 0.1 0.0 10 -1 10 0 AOPC20 AOPF20 Pore diameter (µm) /µm Figure 4.29 Incremental pore size distributions of AOPC20 and AOPF20. 10 1 10 1
As shown in Figure 4.27, the pore size distribution of the magnesia preform MOPC20 sintered at 1300°C was significantly different from that of the other ceramic preforms with the same PFA. In the metal infiltration experiments, an equal pore size distribution was targeted in order to minimize the effect of differing pore size distributions on the comparative study. In order to increase the fraction of finer pores in MOPC20, the sintering temperature was reduced to 800°C with a constant holding time of 2 h. As shown in Figure 4.30, the preform sintered at 800°C shifted the pores to finer sizes while maintaining the bimodal profile. The coarse peak reduced from around 8 µm to about 2 µm and the fine peak reduced from 1.5 to 0.2 µm. The target to reduce the small pore size and to leave the coarse pores as they were, could not be achieved as the coarse pores shifted to smaller sizes when the sintering temperature was reduced. Relative Relative pore pore volume volume () 0.3 0.2 0.1 0.0 10 -1 10 -1 1300°C 800°C 10 0 10 0 Pore diameter (µm) /µm Figure 4.30 Influence of sintering temperature on pore size distribution of MOPC20. The influence of the sintering temperature on the median pore diameter, dHg , and the specific surface area, SsHg , of the MOPC20 preforms is shown in Figure 4.31. As the sintering temperature was lowered from 1300°C to 1200°C, the median pore diameter reduced from 1.50 µm to 0.25 µm and the specific surface area increased from 0.70 m²/g to 3.78 m²/g. 122 10 1 10 1
Pressure Infiltration Behaviour and
ABSTRACT In the pressure infiltrati
CONTENTS 1. INTRODUCTION 1 2. LITER
4.8.3 Evaluation of infiltration be
Symbol Meaning γRv surface energy
Symbol Meaning TYS tensile yield st
these materials are the detrimental
2. LITERATURE REVIEW 2.1. Materials
changes in the oxide film chemistry
or inside the bulk fluid only. Inte
that are most effective in decreasi
initiation stress of 25 %. Further,
Beffort (36) suggested that even th
einforcement interface and reinforc
It is interesting to note that, for
20 Table 2.1 Compilation of the mec
General models to predict fracture
with values observed by others for
The work of adhesion characterises
and vapour, is difficult to evaluat
system Al-Al2O3 is 10 -49 Pa at 700
In the Al-Cu system, although the p
The heat of reaction ΔGr may be es
al. (100) who found non-wetting beh
capillary or threshold pressure has
using constant gas pressure. Infilt
The superficial velocity v0 in the
The permeability K can be expressed
2.4. Preform fabrication Composites
According to Kniewallner (51) even
2.4.3. Foamed preforms Another inte
structure. This is shown schematica
2.5.1. Gas pressure infiltration (G
MMCs infiltrated with an Al-9Mg or
layer oxide films. The Weber number
Long et al. (50) suggested that v0
3. EXPERIMENTAL PROCEDURE The influ
sintered at 1550°C, which represen
using a AVT-Horn (Aalen, Germany) m
squares fit function within the MAP
4.9.2 Compression of preforms The c
Relative preform compression c pr (
decrease depended on the tooling us
Bending stress σ (MPa) / MPa 500 4
4.10.3 Influence of reinforcement t
Significant deformation developed i
a) b) 2 50 2 50 µm µm 2 50 2 50
5. DISCUSSION First the properties
The measured elastic modulus, Edyn
The MMCs showed similar wear with t
interfacial debonding: Peng et al.
The area Sml was derived using data
MMC. Due to the solidification shri
measurements which resulted in a lo
5.1.5 Influence of reactions No rea
5.2. Preform pore formation The tar
kinetics were reported to be rather
The newly formed water vapour led t
In order to achieve minimum porosit
the present work. These pressures w
indicated by zero values of the fre
influence on the pO2,calc. The lowe
during extended holding and acts as
Compared to Hg, the Al melt may con
preforms with IM, Figure 4.67. For
preform compression, cpr , increase
Specific Specific permeability Perm
Permeability (m²) / m² 1x10 -12 1
As the predominant fluid flow was a
In the CP mode, the Preform 1D code
Local Saturation saturation S () lo
listed in Table 5.1 and 5.3 were us
6. CONCLUSIONS 1. An aqueous proces
anged between 112 and 131° for the
8. REFERENCES 1. Altenpohl, D.: Alu
43. Davis, L.C. and Allison, J.E. :
85. Gennes, P.G. : “Wetting: Stat
127. Corbin, S.F., Lee, J. and Qiao
171. Gmelin, L. : Handbook of Inorg
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