1004 A.R. Boccaccini et al. Composites: Part A 32(2001)997-1006 the velocity and deposition rate of the charged colloidal boehmite particles also decreased EPD parameters were optimised in order to achieve fully infiltrated Ni-coated carbon fibre reinforced alumina composites with the minimum amount of excess material being present in the outer regions of the preform. The opti mum deposition voltage and time were determined as 15 V and 400 s, respectively, for full infiltration. The full infiltra- tion resulted in an EPD deposit thickness of >650 um. Using these parameters, it was possible to produce fully infiltrated mats with only a thin(100 um) excess layer This was beneficial as the fibre mats then have a reduced propensity to form large cracks during the drying stage. This cracking is due to the differential shrinkage of the gel network which generates tensile stresses at the surface of the deposits, as mentioned above(see Fig 3) microstructures of composites produced under optimised EPD parameters. Fig. 6(a) shows an SEM micrograph of an EPD-formed green body containing 30 vol% fibre load- ing. High green densities(about 61% of theoretical density) were achieved at 15 V for 400 s. Green density was measured by dividing the mass of the sample by its geome- trically determined volume. It can also be seen in Fig. 6(b) that the Ni-coated carbon fibre preform was fully infiltrated with the boehmite sol. Even in regions where the Ni-coated fibres were nearly touching each other, full impregnation was achieved by the nanosize boehmite powders in a very short time, i. e. 400 s, leading to high-quality green bodies. fibre reinforced alumina matrix composite containing 30 vol% fibre load. The effectiveness of the EPD providing full deposition ing. The fibre preform was infiltrated using an applied voltage of 15 V for between two fibres with a separation of 400-500 nm is 400 s Both(a) high and(b) low magnification micrographs show that the Ni-coated carbon fibre preform was fully infiltrated with the boehmite sol clearly visible in Fig. 6(b). It must be noted that these Even regions where the Ni-coated fibres were nearly touching each other green samples were not polished in order to avoid damaging ve been fully impregnated by the nanosize boehmite particles, leading to the ductile Ni interface. Thus, some cutting effects are high-quality green bodies. visible on the carbon fibres and the matrix. which resulted from the contact with the diamond saw during the very of the aqueous sol dispersion medium, while low slow-speed cutting operation voltages reduced the electrolysis, but they al o neede The subsequent composite preparation involved pres higher deposition times. Thus, a compromise had to be sureless sintering of the green bodies at 1250C for 2 h found and voltage and deposition time were optimised. under N2 atmosphere. a fully infiltrated and dense Voltages higher than 20V were not used. The thickness sintered microstructure is shown in Fig. 7. Sintered of selected electrophoretic deposits, measured from the densities of about 91% of theoretical density were fibre surface, is plotted against the deposition time for measured by using the Archimedes technique. This result different voltages in Fig. 5(b). The formation of the confirms that the electrophoretic processing approach is deposit was very rapid in the first 150 s and then very convenient in terms of obtaining dense samples at increased steadily relatively low sintering temperatures and avoiding the In situ (real time) deposit weight measurements cost-intensive hot-pressing procedure, which has been provided very reliable data to determine accurately the the common practice for the fabrication of fibre rein- deposition rate. The rate of deposition was very high at forced ceramic matrix composites so far he beginning (up to 150 s), and then it started to decrease with increasing deposition time. The decrease in deposition rate was attributed to the increase in the 4 Conclusions resistance of the deposit, as the current diminishes due to the increase in deposit thickness and the removal of A literature review on the application of the EPD tech charged boehmite particles from the sol. As a result of nique in the fabrication of fibre reinforced ceramic and glass the decrease in the potential drop across the suspension, matrix composites was carried out. Since the first studies  '((     (    (     (       -(       (          D   45 D   (  - 2        (     (             M A"% -              6A5        + ( "  %   (         (     -          "(  6A5 %              -        (             (   (       2                (            (                    !#$          (   /&      (     ( (         (      -  & (         6A D  E55     (   - (  &  (   !#$  2  BA5 
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