KAYA et al.: FABRICATION AND CHARACTERISATION OF ALUMINA CERAMIC MATRIX 1193 bon fibres, see Fig. 5(a)and(b), respectively, showed that the metallic Ni coating around the fibres was very △5V homogeneous and with a uniform thickness of about 0.5 um. The carbon fibres were 10-15 um in diam- When EPD is used as a forming technique fo MCs, it is possible to use either constant current or 3 constant voltage conditions. Constant current con- ditions would result in a continually increasing 。=9=3=a882 age due to the increasing resistance of the deposit as it grows in thickness and mass, thus constant voltage conditions were used in this work. Voltages higher than 20V were not used in these experiments in order Electrophoretic Deposition Time(s) to prevent gas bubbles being incorporated within the deposited ceramic matrix. The results from experi- -5V mental trials using the in situ EPD cell design under 000 vacuum are shown in Fig. 6. The graphs in Fig. 6(a) g weight and thickness as a function of deposition time 3300 experiments were performed for duration of up to 200 500 s, as this gave a deposit thickness of about 3 100 o um, which was enough to produce a composite 5 with an acceptable green density. The deposit thick- ness increased with increasing deposition time, as the amount of particles deposited on to the fibres preform Electrophoretic Deposition Time(s) increased. When aqueous based sols are used in EPD 3 experiments, one problem associated with this is the 3 (c) 0 3.2 um electrophoretic thickness as a function of deposition time for different applied voltages. In(c), the deposit formation rate as a function of EPD time under optimised applied voltage of electrolysis of the water. Higher voltages resulted in rapid deposit formation, but also in the undesirable formation and entrapment deposit due to the electrolysis of the aqueous sol dis- persion medium, while low voltages reduced the ele trolysis, but they also needed higher deposition times Thus, a compromise had to be found and voltage and 231pm deposition time were optimised Figure 6a shows that the eight al Most linear with increasing deposition time(up to Fig. 5. FEG SEM micrographs, showing the microstructure of 500 s)and voltage.An oltage of 20 V seems that the metallic Ni coating around the fibres is very homo. ideal according to the I app of deposited material geneous and it has a uniform thickness of 0.5 um. The carbon as shown in Fig. 6(a). However, the deposited matrix fibres are 10-15 um in diameter a result of the gasKAYA et al.: FABRICATION AND CHARACTERISATION OF ALUMINA CERAMIC MATRIX 1193 bon fibres, see Fig. 5(a) and (b), respectively, showed that the metallic Ni coating around the fibres was very homogeneous and with a uniform thickness of about 0.5 µm. The carbon fibres were 10–15 µm in diam￾eter. When EPD is used as a forming technique for CMCs, it is possible to use either constant current or constant voltage conditions. Constant current con￾ditions would result in a continually increasing volt￾age due to the increasing resistance of the deposit as it grows in thickness and mass, thus constant voltage conditions were used in this work. Voltages higher than 20 V were not used in these experiments in order to prevent gas bubbles being incorporated within the deposited ceramic matrix. The results from experi￾mental trials using the in situ EPD cell design under vacuum are shown in Fig. 6. The graphs in Fig. 6(a) and (b) show the results of electrophoretic deposit weight and thickness as a function of deposition time for different applied voltages, respectively. EPD experiments were performed for duration of up to 500 s, as this gave a deposit thickness of about 660 µm, which was enough to produce a composite with an acceptable green density. The deposit thick￾ness increased with increasing deposition time, as the amount of particles deposited on to the fibres preform increased. When aqueous based sols are used in EPD experiments, one problem associated with this is the Fig. 5. FEG SEM micrographs, showing the microstructure of (a) uncoated and (b) Ni-coated carbon fibres. It can be seen that the metallic Ni coating around the fibres is very homo￾geneous and it has a uniform thickness of 0.5 µm. The carbon fibres are 10–15 µm in diameter. Fig. 6. Graphs of the (a) electrophoretic deposit weight and (b) electrophoretic thickness as a function of deposition time for different applied voltages. In (c), the deposit formation rate as a function of EPD time under optimised applied voltage of 15 V is shown. electrolysis of the water. Higher voltages resulted in rapid deposit formation, but also in the undesirable formation and entrapment of bubbles within the deposit due to the electrolysis of the aqueous sol dis￾persion medium, while low voltages reduced the elec￾trolysis, but they also needed higher deposition times. Thus, a compromise had to be found and voltage and deposition time were optimised. Figure 6a shows that the increase in weight is almost linear with increasing deposition time (up to 500 s) and voltage. An applied voltage of 20 V seems ideal according to the amount of deposited material, as shown in Fig. 6(a). However, the deposited matrix microstructure is porous as a result of the gases