D.H. Kuo, w M. Kriven/Materials Science and Engineering A210 (1996)123-134 1550C/5hrs+1600C/6hrs 米 1559C/6h Fig. 7. Scan ctron micrograph of a single-crystal AlO, fiber D of an Al,O/LaPO4 pellet fired at 1550 C for 6 h AdAl,O, ) system having LaPO4(Lp)as an interlayer (bottom) and subsequently fired at 1600C for 6 h(top) and subsequently fired at 1600C for 6 h 1550C. However, chemical reaction occurs after sub- dispersive spectra with those of synthesized pure sequent firing at 1600 C, as shown by the peaks phases. The widths of the LAl and La zones on the corresponding to laAm O18 outer surface of the fiber are approximately 2 um, while In the A12O3 fiber/Al,O3 matrix system with LP as an between the coating and matrix the width is approxi- interlayer, no chemical reaction takes place between mately 7 um. Zone (iii) is an La-rich porous region AL,O, fibers and LP after firing at 1550C in air for 6 with small amounts of Al and P. From the known h. Indentations placed near the LP interlayers in the coating thickness, the porous regions in Fig. 7 can be 1550C composite cause indentation cracks to be located at the positions of the original LP/matrix and deflected by fibers or the LP monazite to chip. Fig. 6 LP/fiber interfaces. Zone(iv)is LP On the other hand, shows such a chipped region around a fiber. It can be the different diffusion configurations in the Al,O3/LP seen that the chipping fracture does not damage the (50: 50 vol %)pellet, after firing at 1600C for 6 h fiber, but is deflected by interfacial debonding. Addi ause a third phase, LAu, to be formed (Fig. 5). Due to tional firing at 1600C for 6 h was performed on the these chemical reactions, the LP/A laminates in this specimen in Fig. 6. Reaction layers and void regions are study were hot pressed only at 1300( formed at the fiber/coating and coating/matrix inter After annealing, XRD and EDS of bulk LP, and faces(Fig. 7). The corresponding energy dispersive EDS of the laminates, indicated that LP was stable, and spectra taken from the zones marked (i)to(iv)in Fig no decomposition or reduction reactions occurred dur 7 are shown in Fig. 8. The compounds formed are ing consolidation by hot pressing identified as LAu in zone(i) and LaAlO,(La)in zone (ii). This is confirmed by comparison of the energy ENERGY (Kev) ENERGY(KeV ENERGY (Kev) Fig. 6. Scanning electron micrograph of a chipped region in single-crystal Al2O, fiber(Ad)/AlO, matrix(A)system having LaPO4 Fig. 8. Energy dispersive spectra taken from the reaction zones LP)as an interlayer, sintered at 1550C for indicated as(i)to(iv) in Fig. 7 between the Al,O, matrix and LaPo interlayD.-H. Kuo, W.M. Kriven /Materials Science and Engineering A210 (1996) 123-134 127 1550"C/6 h.rs + 1600"C/6 hrs A 1550"C/6 hrs 20 25 o A1~ 03 • LaPO 4 A LaAIL1018 A A • • 0 A •A & 0 0 A • A 0 •• • 30 35 40 45 50 20 Fig. 5. XRD of an A1203/LaPO4 pellet fired at 1550 °C for 6 h (bottom) and subsequently fired at 1600 °C for 6 h (top). 1550 °C. However, chemical reaction occurs after sub￾sequent firing at 1600 °C, as shown by the peaks corresponding to LaAll]O~8. In the A1203 fiber/A1203 matrix system with LP as an interlayer, no chemical reaction takes place between AI20 3 fibers and LP after firing at 1550 °C in air for 6 h. Indentations placed near the LP interlayers in the 1550 °C composite cause indentation cracks to be deflected by fibers or the LP monazite to chip. Fig. 6 shows such a chipped region around a fiber. It can be seen that the chipping fracture does not damage the fiber, but is deflected by interfacial debonding. Addi￾tional firing at 1600 °C for 6 h was performed on the specimen in Fig. 6. Reaction layers and void regions are formed at the fiber/coating and coating/matrix inter￾faces (Fig. 7). The corresponding energy dispersive spectra taken from the zones marked (i) to (iv) in Fig. 7 are shown in Fig. 8. The compounds formed are identified as LA11 in zone (i) and LaAIO3 (LA) in zone (ii). This is confirmed by comparison of the energy Fig. 7. Scanning electron micrograph of a single-crystal A1203 fiber (Af)/AI203 matrix (A) system having LaPO4 (LP) as an interlayer, sintered at 1550 °C and subsequently fired at 1600 °C for 6 h. dispersive spectra with those of synthesized pure phases. The widths of the LAtl and LA zones on the outer surface of the fiber are approximately 2/lm, while between the coating and matrix the width is approxi￾mately 7 /~m. Zone (iii) is an La-rich porous region with small amounts of A1 and P. From the known coating thickness, the porous regions in Fig. 7 can be located at the positions of the original LP/matrix and LP/fiber interfaces. Zone (iv) is LP. On the other hand, the different diffusion configurations in the AI203/LP (50:50 vol.%) pellet, after firing at 1600 °C for 6 h, cause a third phase, LA11, to be formed (Fig. 5). Due to these chemical reactions, the LP/A laminates in this study were hot pressed only at 1300 °C. After annealing, XRD and EDS of bulk LP, and EDS of the laminates, indicated that LP was stable, and no decomposition or reduction reactions occurred dur￾ing consolidation by hot pressing. Z [- z AI , , i , ITI iJ~l i i" , i i i i i i i 2 4 6 8 10 ENERGY (KeV) La (ii) 2 4 6 8 10 ENERGY (KeV) .... Fig. 6. Scanning electron micrograph of a chipped region in a single-crystal A1203 fiber (Af)/AI203 matrix (A) system having LaPO4 (LP) as an interlayer, sintered at 1550 °C for 6 h. La (iii) ,i ,i ,i ,i 2 4 6 8 10 ENERGY (KeV) ~ (iv) ENERGY (KeV) Fig. 8. Energy dispersive spectra taken from the reaction zones indicated as (i) to (iv) in Fig. 7 between the A1203 matrix and LaPO4 interlayer