PR Jackson et al. /Materials Science and Engineering A 454-455(2007)590-601 boom Fig. 14. Fracture surfaces of a N610/M/A specimen from billet B15: (a)overall view and (b) magnified view of the fracture surface detail( backscatter SEM image). bright white areas are the monazite coating Cracks initiate within and propagate through the poorly infiltrated 90 fiber layers. reaches-157 MPa Compressive strength of N610/A is three lower than the failure strains obtained in compression tests. For to four times its tensile strength, while compressive modu- both CMCs, compressive creep strains accumulated at 900C lus values remain similar to those obtained in tension. The are at least two orders of magnitude lower than those obtained use of the monazite coating results in 55--60% loss in com- at 1100C pressive strength and in 20-27% decrease in compressive At 1100C, compressive creep rate magnitudes obtained for both composites(ranging from 2. x 10-8 to 9. x 10-8s-) are two orders of magnitude lower than the tensile creep 5.2. Compressive creep-rupture behavior rates obtained for N1O/M/A. Compressive creep strain rate magnitudes of the monazite-containing composite decrease sig- The compressive creep-rupture response of the monazite- nificantly with decreasing temperature. At 900"C, compressive containing composite was evaluated for stress levels ranging creep rate s of both composites are less than -10-s. Com- 75 MPa at 1100C and for a stress level of pressive creep run-out was achieved in all tests regardless of 50MPa at 900C Compressive creep behavior of the N610/A temperature or applied stress. The use of the monazite coating ceramic composite was characterized for stresses in the -50 to had no effect on compressive creep life at temperatures investi- -95 MParange at 900 and for stresses in the-50 to-75 MPa gated. Tensile as well as compressive strength were not affected range at 1100°C by prior compressive creep Both composites exhibit primary and secondary creep regimes at all temperatures investigated. For both N610/M/A 5.3. Composite microstructure and N610/A, compressive creep strain accumulation increases with the magnitude of applied stress at 1100C, but is relatively This investigation confirmed that processing is critical to independent of applied stress at 900C. At 1100C for creep mechanical performance of a CMC. Poor infiltration of the stresses<65 MPa, the N610/M/A composite accumulates larger matrix material into the fibrous layers and presence of matrix- ep strains than N610/A. For all stress levels rich areas between the laminae did not affect tensile properti investigated at 1100C, the compressive creep strains accumu- of the N610/M/A composite, but caused early failures in com- ated by both composites significantly exceed the failure strains pression. The matrix-rich areas and the poorly infiltrated 90o obtained in the compression tests. At 900C, compressive creep fiber layers served as sites of crack initiation and provided weak strains obtained for both composites are an order of magnitude paths for crack propagation600 P.R. Jackson et al. / Materials Science and Engineering A 454–455 (2007) 590–601 Fig. 14. Fracture surfaces of a N610/M/A specimen from billet B15: (a) overall view and (b) magnified view of the fracture surface detail (backscatter SEM image), bright white areas are the monazite coating. Cracks initiate within and propagate through the poorly infiltrated 90◦ fiber layers. reaches −157 MPa. Compressive strength of N610/A is three to four times its tensile strength, while compressive modu￾lus values remain similar to those obtained in tension. The use of the monazite coating results in 55–60% loss in com￾pressive strength and in 20–27% decrease in compressive modulus. 5.2. Compressive creep–rupture behavior The compressive creep–rupture response of the monazite￾containing composite was evaluated for stress levels ranging from −50 to −75 MPa at 1100 ◦C and for a stress level of −50 MPa at 900 ◦C. Compressive creep behavior of the N610/A ceramic composite was characterized for stresses in the −50 to −95 MPa range at 900 ◦C and for stresses in the−50 to−75 MPa range at 1100 ◦C. Both composites exhibit primary and secondary creep regimes at all temperatures investigated. For both N610/M/A and N610/A, compressive creep strain accumulation increases with the magnitude of applied stress at 1100 ◦C, but is relatively independent of applied stress at 900 ◦C. At 1100 ◦C for creep stresses ≤ 65 MPa, the N610/M/A composite accumulates larger compressive creep strains than N610/A. For all stress levels investigated at 1100 ◦C, the compressive creep strains accumu￾lated by both composites significantly exceed the failure strains obtained in the compression tests. At 900 ◦C, compressive creep strains obtained for both composites are an order of magnitude lower than the failure strains obtained in compression tests. For both CMCs, compressive creep strains accumulated at 900 ◦C are at least two orders of magnitude lower than those obtained at 1100 ◦C. At 1100 ◦C, compressive creep rate magnitudes obtained for both composites (ranging from 2.4 × 10−8 to 9.8 × 10−8 s−1) are two orders of magnitude lower than the tensile creep rates obtained for N610/M/A. Compressive creep strain rate magnitudes of the monazite-containing composite decrease sig￾nificantly with decreasing temperature. At 900 ◦C, compressive creep rates of both composites are less than −10−8 s−1. Com￾pressive creep run-out was achieved in all tests regardless of temperature or applied stress. The use of the monazite coating had no effect on compressive creep life at temperatures investi￾gated. Tensile as well as compressive strength were not affected by prior compressive creep. 5.3. Composite microstructure This investigation confirmed that processing is critical to mechanical performance of a CMC. Poor infiltration of the matrix material into the fibrous layers and presence of matrix￾rich areas between the laminae did not affect tensile properties of the N610/M/A composite, but caused early failures in com￾pression. The matrix-rich areas and the poorly infiltrated 90◦ fiber layers served as sites of crack initiation and provided weak paths for crack propagation