312 Journal of the American Ceramic SocieryDavis et al. Vol 86. No. 2 DI 100 mm 100nm BE Monazite Debond YAG- Anina Fiber um Fig. 8. Intense plastic deformation and fine-scale microcracking oating on Al,O,/YAG fiber, Heavily deformed ball of monazite(-10 100nm m diameter) is evident in debond crack at higher magnification (lower Monazite could not be induced (i.e, recrystallization processes were than damage accumulation) was only 35.C for LaPOa, >700C for zircon. This difference was tentatively attributed to Debond the higher stability of isolated POa tetrahedra than isolated Sio units, with less bond-breaking required to crystallize the amor Whether this behavior might be related to ation arter intense mechanical deformation is not clear. Recrystallization of a 400nm YAG-Alumina Fiber surface. Layer adjacent to fiber has dense fine grains(-10-20 1 resembling recrystallized microstructure. Layer further from fiber porous, coarse-grained angular particles diagnostic of cataclastic A20 Matrix tick-slip or stable sliding occurs, with most observations pointing toward inhibition of stick-slip by fine-grained debris. 30 A progression from stick-slip to stable sliding as debris builds up during fiber pushout displacement is possible, with a consequent change in local temperature increases. Unfortu- nately, it is not straightforward to assess any of these effects B)Annealing of Radiation Damage: Monazite is known to recover readily from displacive damage events at near-ambient temperatures, 6, 57 making it extremely resistant to amorphization by radiation damage, and thus an ideal host for containment of actinide or transuranic elements 58, 59 In a recent study bo radiation damage in LaPOa and several related ABO-type phosphates and silicates was monitored as a function of temperature in situ by TEM. Fundamental differences in the amorphization and recrys- RSC02809501 tallization kinetics between the orthophosphates and silicates were bserved. The critical temperature above which amorphization fiber sliding for monazite- coated mullite fiberstick-slip or stable sliding occurs, with most observations pointing toward inhibition of stick-slip by fine-grained debris.30 A progression from stick-slip to stable sliding as debris builds up during fiber pushout displacement is possible, with a consequent change in local temperature increases. Unfortu￾nately, it is not straightforward to assess any of these effects quantitatively. (B) Annealing of Radiation Damage: Monazite is known to recover readily from displacive damage events at near-ambient temperatures,56,57 making it extremely resistant to amorphization by radiation damage, and thus an ideal host for containment of actinide or transuranic elements.58,59 In a recent study,60 radiation damage in LaPO4 and several related ABO4-type phosphates and silicates was monitored as a function of temperature in situ by TEM. Fundamental differences in the amorphization and recrys￾tallization kinetics between the orthophosphates and silicates were observed. The critical temperature above which amorphization could not be induced (i.e., recrystallization processes were faster than damage accumulation) was only 35°C for LaPO4, but 700°C for zircon. This difference was tentatively attributed to the higher stability of isolated PO4 tetrahedra than isolated SiO4 units, with less bond-breaking required to crystallize the amor￾phous structure. Whether this behavior might be related to recrystallization after intense mechanical deformation is not clear. Recrystallization of a Fig. 7. TEM micrograph of monazite smeared onto Al2O3/YAG fiber surface. Layer adjacent to fiber has dense fine grains (10–20 nm scale) resembling recrystallized microstructure. Layer further from fiber has more porous, coarse-grained angular particles diagnostic of cataclastic flow. Fig. 8. Intense plastic deformation and fine-scale microcracking in coating on Al2O3/YAG fiber. Heavily deformed ball of monazite (100 nm diameter) is evident in debond crack at higher magnification (lower right-hand corner). Fig. 9. Schematic of fiber sliding for monazite-coated mullite fiber. 312 Journal of the American Ceramic Society—Davis et al. Vol. 86, No. 2