PR Jackson et al. /Materials Science and Engineering A 454-455(2007)590-601 Table 1 (Model 360FE, Leica)as well as optical microscopy. The SEM Summary of billet properties for the N61O/M/A and the N6l0VA composit specimens were coated with gold or car Billet Fiber volume fraction(%) Density (g/cm) N610/monazite/alumina composite 3. Test procedures All tests were conducted in laboratory air environment at 900 43.0 and 1100C. In all tests, a specimen was heated to the test tem- 44 perature at a rate of 1C/s, and held at temperature for additional BIO 429 BIla 883 30 min prior to testing. Monotonic tension and monotonic com- pression tests were performed in stroke control with a constant B12 displacement rate of 0.05 mm/s In compressive creep-rupture B13 tests specimens were loaded to the creep stress level at the stress N610/alumina composite 839939 rate magnitude of 20 MPa/s Creep run-out was defined as either 100 h at a given creep stress or 50h at creep stress if creep strain rate magnitude remained below 10-9s-I. In each test. stress-strain data were recorded during the loading to the creep stress level as well as during the creep period. Thus, both total B strain and creep strain could be calculated and examined. To B19 2.82 determine the retained tensile(compressive)strength and mod- a billets used in prior work [53]. ulus, specimens that achieved creep run-out were subjected to tensile(compressive) tests to failure at the temperature of the Billets were cut into 16 mm x 126 mm flat rectangular coupons, creep test. In some cases one specimen was tested per test con- which were machined into dog bone-shaped tensile specimens dition. The authors recognize that this is a limited set of data with a 10 mm x 18 mm gage section, and into 20 mm x 126 mm However, this scoping research serves to identify the tempera straight-sided compression specimens. Diamond-grit grinding ture range where the use of monazite coating results in improved was used for billets B1-B8, and the abrasive water-jet machin- creep resistance. Furthermore, results of this exploratory effort ing, for billets B9-B19 can be used to determine whether a more rigorous investigation a servocontrolled mrs mechanical testing machine of the effectiveness of monazite coating in this CMC or in a equipped with hydraulic water-cooled collet grips, a compact different material system should be undertaken wo-zone resistance-heated furnace, and two temperature con- trollers were used in all tests. An mrs TestStar ii digital 4. Results and discussion controller was employed for input signal generation and data acquisition Strain measurement was accomplished with an MTs 4.1. Monotonic tension and monotonic compression high-temperature air-cooled uniaxial extensometer. For elevated ature testing, thermocouples were bonded to the speci- The N610/M/A and N610/A specimens were tested in ten- mens using alumina cement(Zircar) to calibrate the furnace on sion at 900C. In addition, the monazite-containing composite a periodic basis. The furnace controller(using a non-contacting was subjected to tensile test to failure at 23C. Tensile test thermocouple exposed to the ambient environment near the test results are summarized in Table 2, where elastic modulus, ulti- specimen)was adjusted to determine the power setting needed mate tensile strength (UTS)and failure strain are presented for to achieve the desired temperature of the test specimen. The each test temperature. Results from prior work [53] are also determined power setting was then used in actual tests included In compression, the N601/M/A specimens were tested ture surfaces of failed specimens were examined usi at 23, 900 and 1100C, and the N61O/A specimens, at 900 10m Fig. 1. Optical micrographs of the as-processed material showing shrinkage cracks:(a) extensive surface microcracking and (b) interlaminar matrix cracks.592 P.R. Jackson et al. / Materials Science and Engineering A 454–455 (2007) 590–601 Table 1 Summary of billet properties for the N610/M/A and the N610/A composites Billet Fiber volume fraction (%) Density (g/cm3) N610/monazite/alumina composite B1a 44.3 2.55 B2a 39.7 2.48 B4a 40.2 2.49 B5a 43.0 2.50 B9a 44.7 2.58 B10a 42.9 2.58 B11a 41.0 2.53 B12 30.0 2.68 B13 29.1 2.55 B14 26.4 2.58 B15 29.0 2.53 N610/alumina composite B3a 51.6 2.95 B6a 54.8 2.99 B17 35.0 2.73 B18 36.0 2.79 B19 34.5 2.82 a Billets used in prior work [53]. Billets were cut into 16 mm × 126 mm flat rectangular coupons, which were machined into dog bone-shaped tensile specimens with a 10 mm × 18 mm gage section, and into 20 mm × 126 mm straight-sided compression specimens. Diamond-grit grinding was used for billets B1–B8, and the abrasive water-jet machin￾ing, for billets B9–B19. A servocontrolled MTS mechanical testing machine equipped with hydraulic water-cooled collet grips, a compact two-zone resistance-heated furnace, and two temperature con￾trollers were used in all tests. An MTS TestStar II digital controller was employed for input signal generation and data acquisition. Strain measurement was accomplished with an MTS high-temperature air-cooled uniaxial extensometer. For elevated temperature testing, thermocouples were bonded to the speci￾mens using alumina cement (Zircar) to calibrate the furnace on a periodic basis. The furnace controller (using a non-contacting thermocouple exposed to the ambient environment near the test specimen) 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. Frac￾ture surfaces of failed specimens were examined using SEM (Model 360FE, Leica) as well as optical microscopy. The SEM specimens were coated with gold or carbon. 3. Test procedures All tests were conducted in laboratory air environment at 900 and 1100 ◦C. In all tests, a specimen was heated to the test tem￾perature at a rate of 1 ◦C/s, and held at temperature for additional 30 min prior to testing. Monotonic tension and monotonic com￾pression tests were performed in stroke control with a constant displacement rate of 0.05 mm/s. In compressive creep–rupture tests specimens were loaded to the creep stress level at the stress rate magnitude of 20 MPa/s. Creep run-out was defined as either 100 h at a given creep stress or 50 h at creep stress if creep strain rate magnitude remained below 10−9 s−1. In each test, stress–strain data were recorded during the loading to the creep stress level as well as during the creep period. Thus, both total strain and creep strain could be calculated and examined. To determine the retained tensile (compressive) strength and mod￾ulus, specimens that achieved creep run-out were subjected to tensile (compressive) tests to failure at the temperature of the creep test. In some cases one specimen was tested per test con￾dition. The authors recognize that this is a limited set of data. However, this scoping research serves to identify the tempera￾ture 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 monazite coating in this CMC or in a different material system should be undertaken. 4. Results and discussion 4.1. Monotonic tension and monotonic compression The N610/M/A and N610/A specimens were tested in ten￾sion at 900 ◦C. In addition, the monazite-containing composite was subjected to tensile test to failure at 23 ◦C. Tensile test results are summarized in Table 2, where elastic modulus, ulti￾mate tensile strength (UTS) and failure strain are presented for each test temperature. Results from prior work [53] are also included. In compression, the N601/M/A specimens were tested at 23, 900 and 1100 ◦C, and the N610/A specimens, at 900 Fig. 1. Optical micrographs of the as-processed material showing shrinkage cracks: (a) extensive surface microcracking and (b) interlaminar matrix cracks