PR Jackson et al. / Materials Science and Engineering A 454-455(2007)590-601 1E+00 ■N610MA.1100"cT 口N610/MA.11o0℃c, Compression T=900° 态1Ea月·wmm:解 0°c, Compression Ruggles-Wrenn, 2006 0.15 80 MP 0.10 N610A 1E07 0.05 810 a1E° Creep rate magnitude 105 80000 00000 1E-11 ABS CREEP STRESS (MPa) T=900°c for N610/M/A and N610A ceramic composites at 900 and 1100C. from Ruggles-Wrenn et al. [53] are also shown. All tensile data are adjusted for V=0.29. creep strain accumulations were low and steady-state creep rate magnitudes remained below 10-10s-I. It is seen that the com- pressive creep strain magnitudes accumulated in all tests at 900C are an order of magnitude lower than the failure strain magnitude obtained in the compression test. Note that a run- out was achieved in all compressive creep tests conducted at 900C. Conversely, tensile creep run-out was achieved only for 50000 100000 150000 200000 N610/M/A specimens tested at creep stresses s 120 MPa. Minimum creep rate was reached in all tests. Creep strain rate magnitude as a function of applied stress magnitude is Fig 4. Creep curves for NIO/M/Aand NlO/A composites at"C: (a)tensile shown in Fig. 5, where results of previous work [53]are also creep, data from Ruggles-Wrenn et al. [53] and(b) compressive creep included. To facilitate the comparison between the creep prop- erties of specimens with different fiber volume fractions, all creep persists during the first 50h of the creep test. Similar tensile data in Fig. 5 were adjusted for Vf=0. 29. As expected, observations can be made for N610/A. All specimens tested in tensile creep strain rates increase with increasing temperature oppressive creep at 1100C accumulated extensive amounts As demonstrated in prior work [53], at 1100C tensile creep of creep strain. For both composites, compressive creep strain rates of N610/M/A are what may be expected from N610 fibers increases with the magnitude of applied stress. At-50 MPa, the alone. Results in Fig. 5 also show that at 1100C the tensile uncoated fiber composite produced a slightly higher creep strain creep rates are at least two orders of magnitude higher than than the monazite-containing CMC. However, at creep stress the compressive creep rate magnitudes produced at the same levels <-65 MPa, N610/M/A accumulated larger compressive applied stress magnitude. It is recognized that different failure creep strains than N61O/A Compressive creep strain magni- mechanisms are associated with tensile and compressive creep. tudes accumulated in all tests at 1100C significantly exceed Fibers do not play as vital a role in the response of the compos- the failure strain magnitude obtained in the compression test. ite material under compressive creep as they do under tensile All compressive creep tests conducted at 1100C achieved run- creep. While compressive creep rate magnitudes also increase out. Both the monazite-containing composite and the uncoated with rising temperature, the increase is not as dramatic as that in fiber CMC survived 100h of compressive creep at stress levels the case of tensile creep In addition, it is seen that compressive ranging from -50 to -75 MPa. creep rates of the monazite-containing composite are similar At 900C tensile as well as compressive creep curves to those produced by the uncoated fiber CMC. At 900C,ten- obtained for both composites(see Fig. 4)exhibit primary and sile as well as ssive creep strain rate magnitudes of both secondary creep regimes. In both tension and compression, tran- N610/M/A and N61O/A( with the exception of the tensile creep sition from primary to secondary creep occurs early in creep life. rate at 150 MPa)are s 10-8s- In tension, secondary creep continues to failure. Compressive Stress-rupture behavior is summarized in Fig. 6, where creep creep curves in Fig 4(b )indicate that secondary creep is likely to stress magnitude is plotted versus time to rupture at 900 and persist for the duration of the creep life. In both tension and com- 1100C for both composites. Tensile creep-rupture life of the ression, increasing magnitude of creep stress appears to have N610/M/A increases considerably with decreasing temperature little effect on creep strain magnitude, which remains <.05%. At 1100C, tensile creep life was 50,432s(14 h)at the low Compressive creep tests were interrupted after 50h because stress of 40 MPa, and mere 75 s at 120 MPa. At 900C, theP.R. Jackson et al. / Materials Science and Engineering A 454–455 (2007) 590–601 595 Fig. 4. Creep curves for N610/M/A and N610/A composites at 900 ◦C: (a) tensile creep, data from Ruggles-Wrenn et al. [53] and (b) compressive creep. creep persists during the first 50 h of the creep test. Similar observations can be made for N610/A. All specimens tested in compressive creep at 1100 ◦C accumulated extensive amounts of creep strain. For both composites, compressive creep strain increases with the magnitude of applied stress. At −50 MPa, the uncoated fiber composite produced a slightly higher creep strain than the monazite-containing CMC. However, at creep stress levels ≤ −65 MPa, N610/M/A accumulated larger compressive creep strains than N610/A. Compressive creep strain magni￾tudes accumulated in all tests at 1100 ◦C significantly exceed the failure strain magnitude obtained in the compression test. All compressive creep tests conducted at 1100 ◦C achieved run￾out. Both the monazite-containing composite and the uncoated fiber CMC survived 100 h of compressive creep at stress levels ranging from −50 to −75 MPa. At 900 ◦C tensile as well as compressive creep curves obtained for both composites (see Fig. 4) exhibit primary and secondary creep regimes. In both tension and compression, tran￾sition from primary to secondary creep occurs early in creep life. In tension, secondary creep continues to failure. Compressive creep curves in Fig. 4(b) indicate that secondary creep is likely to persist for the duration of the creep life. In both tension and com￾pression, increasing magnitude of creep stress appears to have little effect on creep strain magnitude, which remains ≤ 0.05%. Compressive creep tests were interrupted after 50 h because Fig. 5. Minimum creep rate magnitude as a function of applied stress magnitude 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. All tensile data are adjusted for Vf = 0.29. creep strain accumulations were low and steady-state creep rate magnitudes remained below 10−10 s−1. It is seen that the com￾pressive creep strain magnitudes accumulated in all tests at 900 ◦C are an order of magnitude lower than the failure strain magnitude obtained in the compression test. Note that a run￾out was achieved in all compressive creep tests conducted at 900 ◦C. Conversely, tensile creep run-out was achieved only for N610/M/A specimens tested at creep stresses ≤ 120 MPa. Minimum creep rate was reached in all tests. Creep strain rate magnitude as a function of applied stress magnitude is shown in Fig. 5, where results of previous work [53] are also included. To facilitate the comparison between the creep prop￾erties of specimens with different fiber volume fractions, all tensile data in Fig. 5 were adjusted for Vf = 0.29. As expected, tensile creep strain rates increase with increasing temperature. As demonstrated in prior work [53], at 1100 ◦C tensile creep rates of N610/M/A are what may be expected from N610 fibers alone. Results in Fig. 5 also show that at 1100 ◦C the tensile creep rates are at least two orders of magnitude higher than the compressive creep rate magnitudes produced at the same applied stress magnitude. It is recognized that different failure mechanisms are associated with tensile and compressive creep. Fibers do not play as vital a role in the response of the compos￾ite material under compressive creep as they do under tensile creep. While compressive creep rate magnitudes also increase with rising temperature, the increase is not as dramatic as that in the case of tensile creep. In addition, it is seen that compressive creep rates of the monazite-containing composite are similar to those produced by the uncoated fiber CMC. At 900 ◦C, ten￾sile as well as compressive creep strain rate magnitudes of both N610/M/A and N610/A (with the exception of the tensile creep rate at 150 MPa) are ≤ 10−8 s−1. Stress–rupture behavior is summarized in Fig. 6, where creep stress magnitude is plotted versus time to rupture at 900 and 1100 ◦C for both composites. Tensile creep–rupture life of the N610/M/A increases considerably with decreasing temperature. At 1100 ◦C, tensile creep life was 50,432 s (∼14 h) at the low stress of 40 MPa, and mere 75 s at 120 MPa. At 900 ◦C, the