596 PR Jackson et al. /Materials Science and Engineering A 454-455(2007)590-601 the as-processed material. Both specimens retained 100% of their compressive strength. Furthermore, prior creep appears 250日·M61oMA.o0c. Tensi N610/A, 900C, Compression to have increased compressive modulus. The pre-crept speci ◆N610A,900°c, Tensi mens exhibited higher stiffness values. This indicates that the processing-related cracks may have closed up during com- 9 50 FN610MA, UTS at 110-C pressive creep producing a higher compressive modulus. To evaluate the effects of compressive creep on tensile strength and stiffness, a monazite-containing specimen that achieved a run-out in a-50 MPa compressive creep test at 900C was subjected to a tensile test to failure at that temperature The pre-crept specimen produced a modulus of 68 GPa and strength of 162 MPa, retaining better than 100% of its tensile 100010000100000100000 strength and exhibiting a noticeable increase in modulus. Ten- Time(s) sile stress-strain behavior of the specimen subjected to prior Fig. 6. Creep stress magnitude vs time to rupture for N610/M/A and N610vA compressive creep remained qualitative similar to that of the as- ramic composites at 900 and 1100.C. Tensile data from Ruggles-Wrenn et processed material( see Fig. 8). Retained tensile strength and al. [53] are also shown modulus of the two specimens that reached tensile creep run- out are given in Ref. [53]. Both specimens retained over 90% Table 5 of their tensile strength and at least 90% of their modulus. Prior Retained compressive compressive creep at 1100C ies of the N610/M/A specimens subjected to prior tensile creep had no qualitative effect on tensile stress-strain rength(MPa) modulus(GPa) failure(%) 4.3. Composite microstructure B145 0.13 10 -0.12 Fracture surfaces of the N610/M/A specimens tested in com- pression at 900 and 1100C are shown in ig. 9(d). Brushy 120MPa tensile creep test achieved a run-out. Furthermore, fracture surfaces indicative of fibrous fracture are produced at addition of the monazite coating is seen to significantly improve both temperatures. The optical micrographs in Fig. 9(a and the tensile creep life at 900C. Compressive creep life appears b)reveal the"stepwise"topography of the fracture surfaces to be relatively independent of temperature or applied stress. All obtained at 900oC. The specimen exhibits a fairly large dam- compressive creep tests achieved a run-out. Furthermore, the use age zone of 30-35 mm in length. Extensive delamination is of the monazite coating had little effect on compressive creep readily seen in Fig 9(b). Failure surfaces produced at 1100C life at both temperatures investigated. (see Fig 9(c and d)) are similar to those obtained at 900C, Retained compressive strength and modulus of the speci- although the specimen tested at 1100 C produced somewhat mens that achieved a run-out in -65 and-75 MPa compressive smaller damage zones creep tests at 1100C are summarized in Table 5. Compres- Fracture surfaces of the N610/A specimens tested in sive stress-strain curves obtained for the N610/M/A specimens monotonic compression at 900 and 1100C are presented subjected to prior compressive creep at 1100C are presented Fig I0(a-d). The contrast between the goooC fracture st in Fig. 7 together with the compressive stress-strain curve for faces of the two composites(Figs. 9(a and b)and 10(a and 200 106hat65 T=1100°c T=900°c 0 h at-50 MPa 02 h at-75 MPa Enu Enu As-Processed on doo As-Processed 50 N610/Monazite/Alumina 0 0.05 0.10 0.0 0.4 ABS STRAIN (% STRAIN (% Fig. 7. Effects of prior essive creep at 1100C on compressive Fig 8. Effects of prior compressive creep at 900C on tensile stress-strain tress-strain behavior of N610/M/A ceramic composite. behavior of N610/M/A ceramic composite Results from [53] are also included596 P.R. Jackson et al. / Materials Science and Engineering A 454–455 (2007) 590–601 Fig. 6. Creep stress magnitude vs. time to rupture for N610/M/A and N610/A ceramic composites at 900 and 1100 ◦C. Tensile data from Ruggles-Wrenn et al. [53] are also shown. Table 5 Retained compressive properties of the N610/M/A specimens subjected to prior compressive creep at 1100 ◦C Specimen Creep stress (MPa) Retained strength (MPa) Retained modulus (GPa) Strain at failure (%) B14-5 −65 −113 89 −0.13 B14-4 −75 −102 72 −0.12 120 MPa tensile creep test achieved a run-out. Furthermore, addition of the monazite coating is seen to significantly improve the tensile creep life at 900 ◦C. Compressive creep life appears to be relatively independent of temperature or applied stress. All compressive creep tests achieved a run-out. Furthermore, the use of the monazite coating had little effect on compressive creep life at both temperatures investigated. Retained compressive strength and modulus of the speci￾mens that achieved a run-out in −65 and −75 MPa compressive creep tests at 1100 ◦C are summarized in Table 5. Compres￾sive stress–strain curves obtained for the N610/M/A specimens subjected to prior compressive creep at 1100 ◦C are presented in Fig. 7 together with the compressive stress–strain curve for Fig. 7. Effects of prior compressive creep at 1100 ◦C on compressive stress–strain behavior of N610/M/A ceramic composite. the as-processed material. Both specimens retained 100% of their compressive strength. Furthermore, prior creep appears to have increased compressive modulus. The pre-crept speci￾mens exhibited higher stiffness values. This indicates that the processing-related cracks may have closed up during com￾pressive creep producing a higher compressive modulus. To evaluate the effects of compressive creep on tensile strength and stiffness, a monazite-containing specimen that achieved a run-out in a −50 MPa compressive creep test at 900 ◦C was subjected to a tensile test to failure at that temperature. The pre-crept specimen produced a modulus of 68 GPa and strength of 162 MPa, retaining better than 100% of its tensile strength and exhibiting a noticeable increase in modulus. Ten￾sile stress–strain behavior of the specimen subjected to prior compressive creep remained qualitative similar to that of the as￾processed material (see Fig. 8). Retained tensile strength and modulus of the two specimens that reached tensile creep run￾out are given in Ref. [53]. Both specimens retained over 90% of their tensile strength and at least 90% of their modulus. Prior tensile creep had no qualitative effect on tensile stress–strain behavior. 4.3. Composite microstructure Fracture surfaces of the N610/M/A specimens tested in com￾pression at 900 and 1100 ◦C are shown in Fig. 9(d). Brushy fracture surfaces indicative of fibrous fracture are produced at both temperatures. The optical micrographs in Fig. 9(a and b) reveal the “stepwise” topography of the fracture surfaces obtained at 900 ◦C. The specimen exhibits a fairly large dam￾age zone of 30–35 mm in length. Extensive delamination is readily seen in Fig. 9(b). Failure surfaces produced at 1100 ◦C (see Fig. 9(c and d)) are similar to those obtained at 900 ◦C, although the specimen tested at 1100 ◦C produced somewhat smaller damage zones. Fracture surfaces of the N610/A specimens tested in monotonic compression at 900 and 1100 ◦C are presented Fig. 10(a–d). The contrast between the 900 ◦C fracture sur￾faces of the two composites (Figs. 9(a and b) and 10(a and Fig. 8. Effects of prior compressive creep at 900 ◦C on tensile stress–strain behavior of N610/M/A ceramic composite. Results from [53] are also included