M B. Ruggles-Wrenn et al/ Composites Science and Technology 66(2006)2089-2099 Table I 10.0 ummary of billet properties for the N610/M/A and the N610/A 36.0 fraction (a) Density (g/cc) MonazitelAlumina co …--1 B2 63.0 44. 9088 Fig. 2. Test specimen, dimensions in mm. B10 ment rate of 0.05 mm/s at 23. 900, 1000, 1100 and 1200oC /610/Almina composi Creep-rupture tests were conducted in load control in 595 accordance with Astm standard c 1337 at 900 and 1100C. Specimens were loaded to the creep stress level at the rate of 20 MPa/s. In each test, stress-strain data were recorded during the loading to the creep stress level and the A servocontrolled MTS mechanical testing actual creep period. Thus both total strain and creep strain equipped with hydraulic water-cooled collet grips could be calculated and examined. Creep run-out was pact single-zone resistance-heated furnace, and a defined as 100 h at a given creep stress. To determine the ture controller were used in all tests. An MTS TestStar II retained strength and modulus, specimens that achieved digital controller was employed for input signal generation run-out were subjected to tensile tests to failure at the tem- and data acquisition. Strain measurement was accom- perature of the creep test. One specimen was tested per test plished with an MTS high-temperature air-cooled uniaxial condition. The authors recognize that this is a limited set of extensometer. For elevated temperature testing, thermo- data. However, this scoping research serves to identify the couples were bonded to the specimens using alumina temperature range where the use of monazite coating cement( Zircar)to calibrate the furnace on a periodic basis. results in improved creep resistance. Furthermore, results The furnace controller(using a non-contacting thermocou- of this exploratory effort can be used to determine whether ple exposed to the ambient environment near the test spec- a more rigorous investigation of the effectiveness of mona imen) was adjusted to determine the power setting needed zite coating in this CMC or in a different material system to achieve the desired temperature of the test specimen. should be undertaken The determined power setting was then used in actual tests Fracture surfaces of failed specimens were gold coated 4. Results and discussion and examined using SEM(Model 360FE, Leica)as well as optical microscopy. 4. Monotonic tension 3. Test procedures The N610/M/A specimens were tested at 900, 1000,1100 and 1200C, and the N610/A specimens, at 23, 1100 and All tests were conducted in laboratory air environment. 1200C. Tensile test results are summarized in Table 2 In elevated temperature tests, a specimen was heated to the where elastic modulus, ultimate tensile strength (UTS) test temperature at a rate of lC/s, and held at tempera- and failure strain are presented for each test temperature. ture for additional 15 min prior to testing. Tensile tests The tensile stress-strain curves for both N610/A and were performed in stroke control with a constant displace- N610/M/A composites are shown in Fig 3 10 mm Fig. I. Micrographs of the as-processed material showing shrinkage cracks: (a) extensive surface microcracking and (b) interlaminar matrix cracks.A servocontrolled MTS mechanical testing machine equipped with hydraulic water-cooled collet grips, a com￾pact single-zone resistance-heated furnace, and a tempera￾ture controller were used in all tests. An MTS TestStar II digital controller was employed for input signal generation and data acquisition. Strain measurement was accom￾plished with an MTS high-temperature air-cooled uniaxial extensometer. For elevated temperature testing, thermo￾couples were bonded to the specimens using alumina cement (Zircar) to calibrate the furnace on a periodic basis. The furnace controller (using a non-contacting thermocou￾ple exposed to the ambient environment near the test spec￾imen) was adjusted to determine the power setting needed to achieve the desired temperature of the test specimen. The determined power setting was then used in actual tests. Fracture surfaces of failed specimens were gold coated and examined using SEM (Model 360FE, Leica) as well as optical microscopy. 3. Test procedures All tests were conducted in laboratory air environment. In elevated temperature tests, a specimen was heated to the test temperature at a rate of 1 C/s, and held at tempera￾ture for additional 15 min prior to testing. Tensile tests were performed in stroke control with a constant displace￾ment rate of 0.05 mm/s at 23, 900, 1000, 1100 and 1200 C. Creep-rupture tests were conducted in load control in accordance with ASTM standard C 1337 at 900 and 1100 C. Specimens were loaded to the creep stress level at the rate of 20 MPa/s. In each test, stress–strain data were recorded during the loading to the creep stress level and the actual creep period. Thus both total strain and creep strain could be calculated and examined. Creep run-out was defined as 100 h at a given creep stress. To determine the retained strength and modulus, specimens that achieved run-out were subjected to tensile tests to failure at the tem￾perature of the creep test. One specimen was tested per test condition. The authors recognize that this is a limited set of data. However, this scoping research serves to identify the temperature range where the use of monazite coating results in improved creep resistance. Furthermore, results of this exploratory effort can be used to determine whether a more rigorous investigation of the effectiveness of mona￾zite coating in this CMC or in a different material system should be undertaken. 4. Results and discussion 4.1. Monotonic tension The N610/M/A specimens were tested at 900, 1000, 1100 and 1200 C, and the N610/A specimens, at 23, 1100 and 1200 C. Tensile test results are summarized in Table 2, where elastic modulus, ultimate tensile strength (UTS), and failure strain are presented for each test temperature. The tensile stress–strain curves for both N610/A and N610/M/A composites are shown in Fig. 3. Fig. 1. Micrographs of the as-processed material showing shrinkage cracks: (a) extensive surface microcracking and (b) interlaminar matrix cracks. Table 1 Summary of billet properties for the N610/M/A and the N610/A composites Billet Fiber volume fraction (%) Density (g/cc) N610/Monazite/Alumina composite B1 44.3 2.55 B2 39.7 2.48 B4 40.2 2.49 B5 43.0 2.50 B9 44.7 2.58 B10 42.9 2.58 B11 41.0 2.53 N610/Alumina composite B3 51.6 2.95 B6 54.8 2.99 B8 46.7 2.85 R=50 36.0 63.0 8.0 10.0 5.0 Fig. 2. Test specimen, dimensions in mm. M.B. Ruggles-Wrenn et al. / Composites Science and Technology 66 (2006) 2089–2099 2091