M.B. Ruggles-Wrenn et al /Composites Science and Technology 66(2006)2089-2099 failure strain at 1200C is approximately 4.5 times that at ummary of tensile properties for the N610/M/A and the N6IO/A 1100 %( composites It is important to note that in all tension tests, as well as Specimen Temperature Elastic modulus UTS Failure strain in all other tests reported herein, the failure occurred within GPa) the gage section of the extensometer N10/ Monazite/Alumina composite 0.3l 4. 2. Creep rupture B2-1 15 1200 130 142 Results of the creep-rupture tests are summarized in N610/Almina composite Table 3, where creep strain accumulation and time to rup l17 0.09 ture are shown for each test temperature and applied stress 105 level. Creep curves obtained for the coated fiber composite at 1100C are presented in Fig. 4. Creep curves obtained at 900C for N610/M/A and N610/A are shown in Figs. 5(a) The stress-strain curves obtained for the uncoated fiber and(b), respectively. The time scale in Figs. 4(a)and 5 is composite at 23 and 1100C are nearly linear to failure. reduced in order to clearly show the creep curves produced all suggest a monolithic fracture behavior with no toughen- 900 C the uncoated fiber composite did not achieve a ing from fibers. For temperatures <1100C and strains run-out even for a low stress of 73 MPa. Recognizing that <0.1%, the stress-strain behavior of the N610/M/A com- increase in temperature would result in reduced creep life, posite is also nearly linear elastic. However, as the strain the N610/A was not expected to achieve a run-out at exceeds 0. 1% the stress-strain curves depart from linearity. 1100 oC for stresses >75 MPa. and was therefore not The subsequent non-linear behavior, indicative of progres- tested at that temperature sive matrix cracking and crack deflection, continues until Creep curves produced by N610/M/A at 1100C exhibit failure. The fracture surfaces show considerable fiber pull primary, secondary and tertiary creep regimes. Transition decrease with increasing temperature, while the failure ately. For stresses <80 MPa, secondary creep persists for strain remains fairly temperature-independent. Results in n70% of the creep life before transitioning to tertiary Table 2 reveal that at 1100C, the addition of the monazite creep. However, for stresses >100 MPa, secondary creep coating results in a nearly 50% increase in UTS. However, transitions to tertiary creep during the first third of the this increase in strength is accompanied by a 34% decrease creep life. Creep strain accumulation decreases witl in modulus and a threefold increase in failure strain increasing applied stress. While at 40 MPa creep strain The stress-strain behavior of both composites changes a significant 7.66%, at 120 MPa creep strain is only 0.7% It is noteworthy that at 1100C, for stress levels in the gely nonlinear, the strength and modulus decrease signif 40-120 MPa range, the accumulated creep strains signifi- cantly,while failure strains increase. The increase in cantly exceed the failure strain obtained in the tension test temperature from 1100 to 1200C causes a 10% loss in The creep run-out, defined as survival of 100 h at a given UTS and a 57% loss in modulus for the uncoated fiber composite, and a 17 loss in UTS and a 34% loss in mod. creep stress, was not achieved ulus for the coated fiber composite. For both materials the Table 3 Summary of creep-rupture results for the N610/M/A and the N610/A composites Specimen Temperature stress Creep strain Time to 900c rupture(s Ng10/Monazite/Alumina cor 15023c 1100°c 7.66 1200°c B4-2 1100c 1.58 B4-3 l100 1200°c B9. 0.05 63.060 Bl0-1 0.04 522,3652 Bl0-2 432,1752 N610/Monazite/ Alumina B51 0.05 BIl-I l40 0.03 BIl-2 150 0.75 STRAIN (% N610/Almina composite B6-1 Fig. 3. Tensile stress-strain curves for N610/A and N610/M/A ceram B6-2 0.03 19,995 composites at various temperatures.The stress–strain curves obtained for the uncoated fiber composite at 23 and 1100 C are nearly linear to failure. The linear behavior, low UTS, and flat fracture surface all suggest a monolithic fracture behavior with no toughen￾ing from fibers. For temperatures 61100C and strains 60.1%, the stress–strain behavior of the N610/M/A com￾posite is also nearly linear elastic. However, as the strain exceeds 0.1% the stress–strain curves depart from linearity. The subsequent non-linear behavior, indicative of progres￾sive matrix cracking and crack deflection, continues until failure. The fracture surfaces show considerable fiber pull out. For both composites, the elastic modulus and UTS decrease with increasing temperature, while the failure strain remains fairly temperature-independent. Results in Table 2 reveal that at 1100 C, the addition of the monazite coating results in a nearly 50% increase in UTS. However, this increase in strength is accompanied by a 34% decrease in modulus and a threefold increase in failure strain. The stress–strain behavior of both composites changes dramatically at 1200 C. The stress–strain curves are lar￾gely nonlinear, the strength and modulus decrease signifi- cantly, while failure strains increase. The increase in temperature from 1100 to 1200 C causes a 10% loss in UTS and a 57% loss in modulus for the uncoated fiber composite, and a 17% loss in UTS and a 34% loss in mod￾ulus for the coated fiber composite. For both materials the failure strain at 1200 C is approximately 4.5 times that at 1100 C. It is important to note that in all tension tests, as well as in all other tests reported herein, the failure occurred within the gage section of the extensometer. 4.2. Creep rupture Results of the creep-rupture tests are summarized in Table 3, where creep strain accumulation and time to rup￾ture are shown for each test temperature and applied stress level. Creep curves obtained for the coated fiber composite at 1100 C are presented in Fig. 4. Creep curves obtained at 900 C for N610/M/A and N610/A are shown in Figs. 5(a) and (b), respectively. The time scale in Figs. 4(a) and 5 is reduced in order to clearly show the creep curves produced at higher stress levels. Results in Table 3 reveal that at 900 C the uncoated fiber composite did not achieve a run-out even for a low stress of 73 MPa. Recognizing that increase in temperature would result in reduced creep life, the N610/A was not expected to achieve a run-out at 1100 C for stresses P75 MPa, and was therefore not tested at that temperature. Creep curves produced by N610/M/A at 1100 C exhibit primary, secondary and tertiary creep regimes. Transition from primary to secondary creep occurs almost immedi￾ately. For stresses 680 MPa, secondary creep persists for 70% of the creep life before transitioning to tertiary creep. However, for stresses P100 MPa, secondary creep transitions to tertiary creep during the first third of the creep life. Creep strain accumulation decreases with increasing applied stress. While at 40 MPa creep strain is a significant 7.66%, at 120 MPa creep strain is only 0.7%. It is noteworthy that at 1100 C, for stress levels in the 40–120 MPa range, the accumulated creep strains signifi- cantly exceed the failure strain obtained in the tension test. The creep run-out, defined as survival of 100 h at a given creep stress, was not achieved. Table 2 Summary of tensile properties for the N610/M/A and the N610/A composites Specimen Temperature (C) Elastic modulus (GPa) UTS (MPa) Failure strain (%) N610/Monazite/Alumina composite B9-1 900 83 180 0.31 B5-1 1000 78 162 0.28 B2-1 1100 76 157 0.34 B1-1 1200 50 130 1.42 N610/Alumina composite B3-1 23 129 117 0.09 B3-2 1100 116 105 0.11 B8-1 1200 49 95 0.46 0 50 100 150 200 0.00 0.25 0.50 0.75 1.00 1.25 1.50 STRAIN (%) STRESS (MPa) 1200˚C 1200˚C N610/Monazite/Alumina N610/Alumina 1100˚C 1100˚C 900˚C 23˚C 1000˚C Fig. 3. Tensile stress–strain curves for N610/A and N610/M/A ceramic composites at various temperatures. Table 3 Summary of creep-rupture results for the N610/M/A and the N610/A composites Specimen Temperature (C) Creep stress (MPa) Creep strain (%) Time to rupture (s) N610/Monazite/Alumina composite B4-1 1100 40 7.66 50,432 B4-2 1100 80 3.36 1,452 B2-2 1100 100 1.58 360 B4-3 1100 120 0.70 75 B9-2 1000 80 0.05 63,060 B10-1 900 80 0.04 522,365a B10-2 900 120 0.04 432,175a B5-1 900 130 0.05 40,655 B11-1 900 140 0.03 54,075 B11-2 900 150 0.03 805 N610/Alumina composite B6-1 900 73 0.06 350,055 B6-2 900 80 0.03 19,995 a Run-out. 2092 M.B. Ruggles-Wrenn et al. / Composites Science and Technology 66 (2006) 2089–2099