D.-H. Kuo, W M, Kriven/ Materials Science and Engineering A210(1996)123-134 mammary of four point fexural strengths of single phase and laminates Y3AlsO12 LaAlO,s LaPO4/Al,O, LaPO/YAl O LaPO4/laA hickness (u allot shear-lag approaches are very similar for the YaG fiber reaction is the P+ ions remaining in the La+-deficient system(100 MPa) and Al2O3 fiber system(128 MPa). LP coating after the La+ has diffused into the Al,O3 Both systems have similar test sizes and coating thick phase, formed vaporizable P2Os and created porous nesses.The average LP coating thickness is approxi- voids. Vaporization of phosphorus in the form of P2O. mately 6.5 um for the Al O3 fiber system and results in no detectable P in zones ()and (ii).The approximately 9 um for the YAG fiber system. The results in Fig. 7 also suggest that La+ ions diffuse latter has a lower interfacial shear strength. Table 3 more slowly in single-crystal Al,O, than in polycrys- gives a summary of the experimental pushout results. talline Al,O3. This is confirmed by the relative widths of Scanning electron micrographs of the pushed-out fibers the LAu and LA layers at the fiber/coating(approxi- are shown in Fig 17. Because of the formation of LAu mately 2 um)and coating/matrix(approximately 7 um) between the Al,O3 fibers and the Lp coating, deter- interfaces respectively mined from the chemical compatibility study, EDS The reaction between Al,O and LP was also noted analysis was used to examine the wall of the pushed-out by Morgan et al. [12]. After prolonged firing at 1600C fibers. The result confirms that interfacial debonding for 24 h, small amounts of B-alumina/ magnetoplumbite occurs between the thin LAu layer on the Al,, fiber platelets were observed in localized regions of the alu surface and the lp coating. mina layers in multilayered composites. They pointed out that the reaction was confined to the near-surface egion and was very sensitive to impurities which could 4. Discussion Phenate from raw materials or from the furnace atmo- orig 4.1. Chemical compatibility 4.2. Microstructure of laminated composites The observation of compound formation in zones of finite thickness in Fig. 7 indicates that interdiffusion The laminated composites show flat, stable inter- occurs between A12O3 and LP. a possible source of faces, and no residual stress-induced cracking after 题1243a,Qg四 Fig. 12. Scanning electron micrograph of interfacial delamination in Fig. 13. Enlarged micrograph of interfacial delamination in the a notched LaPO/LaAl, O1s laminate after a flexural test. indented laminate shown in Fig. 10(c)(marked by arrows)130 D.-H. Kuo, W.M. Kriven / Materials Science and Engineering A210 (1996) 123-134 Table 2 Summary of four point flexural strengths of single phase and laminates YsA150~2 LaAll i O t 8 LaPO4/AI2Os LaPO4/YsAI5012 LaPO4/LaAll IO1 s LaPO4 N/A (vol.%) LaPO4 N/A thickness (#m) Strength 180 (MPa) One standard 14 deviation (MPa) N/A 26 44 42 N/A 25 30 25 217 79 107 122 3 16 13 20 shear-lag approaches are very similar for the YAG fiber system (100 MPa) and A1203 fiber system (128 MPa). Both systems have similar test sizes and coating thick￾nesses. The average LP coating thickness is approxi￾mately 6.5 /tm for the A1203 fiber system and approximately 9 /zm for the YAG fiber system. The latter has a lower interfacial shear strength. Table 3 gives a summary of the experimental pushout results. Scanning electron micrographs of the pushed-out fibers are shown in Fig. 17. Because of the formation of LA11 between the A1203 fibers and the LP coating, deter￾mined from the chemical compatibility study, EDS analysis was used to examine the wall of the pushed-out fibers. The result confirms that interfacial debonding occurs between the thin LA~ layer on the A1203 fiber surface and the LP coating. 4. Discussion 4.1. Chemical compatibility The observation of compound formation in zones of finite thickness in Fig. 7 indicates that interdiffusion occurs between A1203 and LP. A possible source of reaction is the p5 + ions remaining in the La 3 ÷ -deficient LP coating after the La 3 ÷ has diffused into the A12Oa phase, formed vaporizable P205 and created porous voids. Vaporization of phosphorus in the form of P205 results in no detectable P in zones (i) and (ii). The results in Fig. 7 also suggest that La 3+ ions diffuse more slowly in single-crystal AI203 than in polycrys￾talline AI203. This is confirmed by the relative widths of the LAI~ and LA layers at the fiber/coating (approxi￾mately 2/~m) and coating/matrix (approximately 7/tm) interfaces respectively. The reaction between A1203 and LP was also noted by Morgan et al. [12]. After prolonged firing at 1600 °C for 24 h, small amounts of fl-alumina/magnetoplumbite platelets were observed in localized regions of the alu￾mina layers in multilayered composites. They pointed out that the reaction was confined to the near-surface region and was very sensitive to impurities which could originate from raw materials or from the furnace atmo￾sphere. 4.2. Microstructure of laminated composites The laminated composites show flat, stable inter￾faces, and no residual stress-induced cracking after Fig. 12. Scanning electron micrograph of interfacial delamination in Fig. 13. Enlarged micrograph of interfacial delamination in the a notched LaPOa/LaAI~tO~s laminate after a flexural test. indented laminate shown in Fig. 10(c) (marked by arrows)