PR Jackson et al. /Materials Science and Engineering A 454-455(2007)590-601 (a) (b) 5 mm 4 mm mm 4 m Fig 10. Fracture surfaces of N601/A specimens tested in compression at: (a)900C.( b)900C-side view, (c)1100"C and (d)1100C-side view values suggested that composite microstructure of billet B15 into the 90 fiber layer, where they self-arrest. A magnified may be different from that of billet B14. Optical micrographs view of the fracture surface detail in Fig. 13(b) shows sepa- of the as-processed material from billets B15(Fig. 11)and B14 rate cracks initiating between the laminae, propagating along (Fig. 12)reveal significant differences in microstructure. The angled paths into the 90 fiber layer, and finally self-arresting cross-section of the b 15 material in Fig. lI shows thick matrix Note that no matrix-rich areas are visible in micrographs in bands located between the fibrous layers. In contrast, micro- Fig 13. A much different failure mechanism is observed in the graph of the as-processed material from B 14 in Fig 12 shows specimen from billet B15(see Fig. 14). Cracks initiate within only a few isolated matrix-rich areas and good infiltration of the and propagate directly through the 90 fiber layers. Unlike the matrix material into the 900 fiber I short self-arresting cracks seen in the B14 specimens, cracks The thick matrix-rich layers found in billet B15 together with seen in Fig. 14(a) propagate to considerable lengths before eas devoid of matrix in the fibrous layers suggest a process dissipating their energy. A higher magnification view of the frac control problem. Further examination of the fracture surfaces of ture surface of the B15 specimen in Fig. 14(b)shows a crack pecimens from billets B14 and B15 reveals that the presence propagating through the 90 fiber layer. Apparent differences of the matrix-rich regions and poor infiltration of the matrix in microstructure resulted in different failure mechanisms in material into the fibrous layers indeed caused early compr N610/M/A specimens from billets B14 and B15, and caused sive failures and low compressive strength. Fracture surfaces of early compression failures of the B15 specimens. Poor infil- N610/M/A specimens from billets B14 and B15 presented in tration of the matrix material into the fibrous layers in billet Figs. 13 and 14, respectively, suggest different failure mech- B15 may have been caused by either fiber bridging due to the nisms. It is seen in Fig. 13(a) that in B14 specimens the application of fiber coating or by high viscosity of the matrix cracks initiate between the laminae then propagate at an angle slurry598 P.R. Jackson et al. / Materials Science and Engineering A 454–455 (2007) 590–601 Fig. 10. Fracture surfaces of N601/A specimens tested in compression at: (a) 900 ◦C, (b) 900 ◦C—side view, (c) 1100 ◦C and (d) 1100 ◦C—side view. values suggested that composite microstructure of billet B15 may be different from that of billet B14. Optical micrographs of the as-processed material from billets B15 (Fig. 11) and B14 (Fig. 12) reveal significant differences in microstructure. The cross-section of the B15 material in Fig. 11 shows thick matrix bands located between the fibrous layers. In contrast, micro￾graph of the as-processed material from B14 in Fig. 12 shows only a few isolated matrix-rich areas and good infiltration of the matrix material into the 90◦ fiber layer. The thick matrix-rich layers found in billet B15 together with areas devoid of matrix in the fibrous layers suggest a process control problem. Further examination of the fracture surfaces of specimens from billets B14 and B15 reveals that the presence of the matrix-rich regions and poor infiltration of the matrix material into the fibrous layers indeed caused early compres￾sive failures and low compressive strength. Fracture surfaces of N610/M/A specimens from billets B14 and B15 presented in Figs. 13 and 14, respectively, suggest different failure mech￾anisms. It is seen in Fig. 13(a) that in B14 specimens the cracks initiate between the laminae then propagate at an angle into the 90◦ fiber layer, where they self-arrest. A magnified view of the fracture surface detail in Fig. 13(b) shows sepa￾rate cracks initiating between the laminae, propagating along angled paths into the 90◦ fiber layer, and finally self-arresting. Note that no matrix-rich areas are visible in micrographs in Fig. 13. A much different failure mechanism is observed in the specimen from billet B15 (see Fig. 14). Cracks initiate within and propagate directly through the 90◦ fiber layers. Unlike the short self-arresting cracks seen in the B14 specimens, cracks seen in Fig. 14(a) propagate to considerable lengths before dissipating their energy. A higher magnification view of the frac￾ture surface of the B15 specimen in Fig. 14(b) shows a crack propagating through the 90◦ fiber layer. Apparent differences in microstructure resulted in different failure mechanisms in N610/M/A specimens from billets B14 and B15, and caused early compression failures of the B15 specimens. Poor infil￾tration of the matrix material into the fibrous layers in billet B15 may have been caused by either fiber bridging due to the application of fiber coating or by high viscosity of the matrix slurry