K K. Chawla et al. Journal of the European Ceramic Society 20(2000)551-559 125 and 150 um and a finish of 0. 1 um, perpendicular to the debonding observed in 10-dip coated composite. Fig the fiber orientation. A cylindrical indentor with a 114.3 3 shows that cracks passed through the alumina matrix um diameter was used to apply a load at a constant monazite interface and debonded the monazite/Saphi displacement rate of 0.3125 um/s through the debond- kon fiber interface. Comparatively, monazite/Saphikon ing and sliding stages fiber interface was weaker than the monazite/alumina matrix interface. Fig 4 shows two indentations made by 98N load in the matrix on the two sides of a five-dir 3. Results and discussion coated fiber. One can see smooth and continuous inter. facial debonding In Fig. 4(b)and(c), high magnification Fig. I shows the different parameters that should be secondary electron images show clearly the crack in alu- considered in the precursor design of a coating. In the mina penetrating the monazite interphase and debond- present case, the ethanol-based solution was clear and ing at the monazite/Saphikon fiber interface. The bright relatively stable. It had a low viscosity and gave a high area in the backscattered electron image [ Fig 4(c)) is the ield of monazite(160 g/). The monazite coating formed monazite, which separated from the Saphikon fiber below 600oC. It showed good wetting and film forming Clearly, interfacial debonding occurred at the Saphikon characteristics. Fig. 2. shows the X-ray u: ndicating the polycrystalline alumina/monazite interface. This is con- diffraction pat fiber/monazite interface, which was less rough than formation of stoichiometric lanthanum phosphate. sistent with the Morgan and Marshall analysis of inter- Indentation cracks, produced in the matrix with 98n facial debonding in this system. 7 For the 10-dip coate force, showed interfacial debonding. However, in the fiber composite, when two indentations with 98 N force case of five-dip coating, the interfacial debonding was were put in the matrix on the two sides of the fiber,as more clear and larger areas were debonded compared to seen in Fig. 5, interfacial debonding was also observed However, the crack surface was rough. It was not possi ble to determine which interface, if any, debonded It is Low Temperature High Yield SEM cursor Wetting Saphikon Solution Efficient Drying Characteristics Fig l. Various parameters to be considered in the coating precursor Saphikon Alumina Monazite interface with cracks produced by a 98N indentation in the matrix: (a) low magnification SEM image and(b) high magnification SEM image (98 N load, 15 s). Note that cracks passed through the alumina matrix/ Fig. 2. X-ray diffraction pattern showing the formation of stoichio- monazite interface and debonded the monazite/Saphikon fiber inter- metric LaPO4 face125 and 150 mm and a ®nish of 0.1 mm, perpendicular to the ®ber orientation. A cylindrical indentor with a 114.3 mm diameter was used to apply a load at a constant displacement rate of 0.3125 mm/s through the debond￾ing and sliding stages. 3. Results and discussion Fig. 1 shows the di€erent parameters that should be considered in the precursor design of a coating. In the present case, the ethanol-based solution was clear and relatively stable. It had a low viscosity and gave a high yield of monazite (160 g/l). The monazite coating formed below 600C. It showed good wetting and ®lm forming characteristics. Fig. 2. shows the X-ray di€raction pat￾tern of the coating obtained from the sol indicating the formation of stoichiometric lanthanum phosphate. Indentation cracks, produced in the matrix with 98 N force, showed interfacial debonding. However, in the case of ®ve-dip coating, the interfacial debonding was more clear and larger areas were debonded compared to the debonding observed in 10-dip coated composite. Fig. 3 shows that cracks passed through the alumina matrix/ monazite interface and debonded the monazite/Saphi￾kon ®ber interface. Comparatively, monazite/Saphikon ®ber interface was weaker than the monazite/alumina matrix interface. Fig. 4. shows two indentations made by 98 N load in the matrix on the two sides of a ®ve-dip coated ®ber. One can see smooth and continuous inter￾facial debonding. In Fig. 4(b) and (c), high magni®cation secondary electron images show clearly the crack in alu￾mina penetrating the monazite interphase and debond￾ing at the monazite/Saphikon ®ber interface. The bright area in the backscattered electron image [Fig. 4(c)] is the monazite, which separated from the Saphikon ®ber. Clearly, interfacial debonding occurred at the Saphikon ®ber/monazite interface, which was less rough than polycrystalline alumina/monazite interface. This is con￾sistent with the Morgan and Marshall analysis of inter￾facial debonding in this system.7 For the 10-dip coated ®ber composite, when two indentations with 98 N force were put in the matrix on the two sides of the ®ber, as seen in Fig. 5, interfacial debonding was also observed. However, the crack surface was rough. It was not possi￾ble to determine which interface, if any, debonded. It is Fig 1. Various parameters to be considered in the coating precursor design. Fig. 2. X-ray di€raction pattern showing the formation of stoichio￾metric LaPO4. Fig. 3. Interfacial debonding at the (10-dip) monazite/Saphikon ®ber interface with cracks produced by a 98 N indentation in the matrix: (a) low magni®cation SEM image and (b) high magni®cation SEM image (98 N load, 15 s). Note that cracks passed through the alumina matrix/ monazite interface and debonded the monazite/Saphikon ®ber inter￾face. K.K. Chawla et al. / Journal of the European Ceramic Society 20 (2000) 551±559 553