M.B. Ruggles-Wrenn et al. Composites Science and Technology 66(2006)2089-2099 0.25 N610/Monazite/Alur 100c N610/Monazite/Alumina e0.15 120 MPa 0.10 140 MPa 150 MPa 0.05 120 MPa 40 MPa 100 0.00 2000040000 80000100000 Time(s) 610/Alumina (b) R5.0 e0.1 80 MPa 方0.10 0.05 80 MPa 73 MPa 100002000030000400005000060000 0.00 4000060000 Time(s Fig 4. Creep strain vs time curves for the N610/M/A ceramic composite at 1100C: (a)time scale is reduced to clearly show creep curves obtained Fig. 5. Creep strain vs time curves at 900C for:(a)N610/Monazite/ at stress levels >100 MPa and(b) time scale chosen to show creep strai Alumina and(b) N610/Alumin ccumulated at 40 MPa ble differences between the creep strains accumulated at dif Because creep rupture of this CMC is likely dominated ferent stress levels together with the inherent data scatter by creep of Nextel 610 fibers, it is useful to compare results account for an atypical order of the creep curves in presented here with those reported by Zawada et al. [37]for Fig. 5(a)(i.e 130 MPa creep curve showing slightly higher N610/AS. At 1100C and creep stress levels of 50 and strains than the 140 MPa curve). Note that all creep strains 75 MPa, N610/AS did not exhibit tertiary creep and conse- are an order of magnitude lower than the failure strain quently accumulated considerably lower creep strains. obtained in the tension test at 900C. Creep behavior of However, rupture times were comparable to those obtained the uncoated fiber composite is qualitatively similar to that for N610/M/A. Furthermore, N610/AS did not achieve a of the coated fiber CMC. Likewise, creep strains are similar run-out even for stress as low as 50 MPa. At 1000C, to those accumulated by the coated fiber composite N610/AS exhibited improved creep resistance, achieving Minimum creep rate was reached in all tests. Creep a run-out at 75 MPa. Conversely, creep resistance of the strain rate as a function of applied stress is shown in N610/M/A composite remained poor at 1000C. A scop- Fig. 6, where results of the present investigation are plotted ing creep test conducted at 1000C and 80 MPa failed after together with the data from Wilson and Visser [40]for 17.5h. Short creep lives at 1000 and 1100C, and exces- Nextel 610 fibers, Zawada et al. [37] for a N610/AS com- a ely large creep strains at 1100C reveal poor creep per- posite, and Casas and Martinez-Esnaola [41] for a Nextel mance, making this material unacceptable for 610/Mox composite. To further facilitate comparison applications invol sustained loading at temperatures between the creep properties of the fibers and the compos- >1000C. Therefore, creep performance at 900C was ites, the Nextel 610 fiber data adjusted for V=0.2 and examined Vr=0. 15 (volume fractions of the on-axis fibers in the A It is seen in Fig. 5(a) that the creep curves obtained for N610/M/A and N610/AS composites, respectively), are 10/M/A at 900C exhibit primary and secondary creep also shown regimes. Transition from primary to secondary creep As expected, the creep strain rates increase with increas- ure.Increasing creep stress appears to have little effect on pplied stress as well as with increasing temperature.At occurs early in creep life. Secondary creep continues to fail- ing creep rates of N610/M/A are what may creep strain(see Table 3), which remains <0.05%. Negligi- expected from Nextel 610 fibers alone. Experimental resuBecause creep rupture of this CMC is likely dominated by creep of Nextel 610 fibers, it is useful to compare results presented here with those reported by Zawada et al. [37] for N610/AS. At 1100 C and creep stress levels of 50 and 75 MPa, N610/AS did not exhibit tertiary creep and conse￾quently accumulated considerably lower creep strains. However, rupture times were comparable to those obtained for N610/M/A. Furthermore, N610/AS did not achieve a run-out even for stress as low as 50 MPa. At 1000 C, N610/AS exhibited improved creep resistance, achieving a run-out at 75 MPa. Conversely, creep resistance of the N610/M/A composite remained poor at 1000 C. A scop￾ing creep test conducted at 1000 C and 80 MPa failed after 17.5 h. Short creep lives at 1000 and 1100 C, and exces￾sively large creep strains at 1100 C reveal poor creep per￾formance, making this material unacceptable for applications involving sustained loading at temperatures P1000 C. Therefore, creep performance at 900 C was examined. It is seen in Fig. 5(a) that the creep curves obtained for N610/M/A at 900 C exhibit primary and secondary creep regimes. Transition from primary to secondary creep occurs early in creep life. Secondary creep continues to fail￾ure. Increasing creep stress appears to have little effect on creep strain (see Table 3), which remains 60.05%. Negligi￾ble differences between the creep strains accumulated at dif￾ferent stress levels together with the inherent data scatter, account for an atypical order of the creep curves in Fig. 5(a) (i.e. 130 MPa creep curve showing slightly higher strains than the 140 MPa curve). Note that all creep strains are an order of magnitude lower than the failure strain obtained in the tension test at 900 C. Creep behavior of the uncoated fiber composite is qualitatively similar to that of the coated fiber CMC. Likewise, creep strains are similar to those accumulated by the coated fiber composite. Minimum creep rate was reached in all tests. Creep strain rate as a function of applied stress is shown in Fig. 6, where results of the present investigation are plotted together with the data from Wilson and Visser [40] for Nextel 610 fibers, Zawada et al. [37] for a N610/AS com￾posite, and Casas and Martinez-Esnaola [41] for a Nextel 610/Umox composite. To further facilitate comparison between the creep properties of the fibers and the compos￾ites, the Nextel 610 fiber data adjusted for Vf = 0.2 and Vf = 0.15 (volume fractions of the on-axis fibers in the N610/M/A and N610/AS composites, respectively), are also shown. As expected, the creep strain rates increase with increas￾ing applied stress as well as with increasing temperature. At 1100 C, creep rates of N610/M/A are what may be expected from Nextel 610 fibers alone. Experimental results 0.0 0.5 1.0 1.5 2.0 0 100 200 300 400 Time (s) Strain (%) N610/Monazite/Alumina T = 1100˚C 80 MPa 100 MPa 120 MPa 40 MPa 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 0 10000 20000 30000 40000 50000 60000 Time (s) Strain (%) N610/Monazite/Alumina T = 1100˚C 80 MPa 40 MPa (a) (b) Fig. 4. Creep strain vs time curves for the N610/M/A ceramic composite at 1100 C: (a) time scale is reduced to clearly show creep curves obtained at stress levels P100 MPa and (b) time scale chosen to show creep strain accumulated at 40 MPa. 0.00 0.05 0.10 0.15 0.20 0.25 0 20000 40000 60000 80000 100000 Time (s) Strain (%) N610/Monazite/Alumina T = 900˚C 80 MPa 120 MPa 140 MPa 130 MPa 150 MPa 0.00 0.05 0.10 0.15 0.20 0.25 0 20000 40000 60000 80000 100000 Time (s) Strain (%) N610/Alumina T = 900˚C 80 MPa 73 MPa (a) (b) Fig. 5. Creep strain vs time curves at 900 C for: (a) N610/Monazite/ Alumina and (b) N610/Alumina. M.B. Ruggles-Wrenn et al. / Composites Science and Technology 66 (2006) 2089–2099 2093