H. Mei et al Scripta Materialia 54(2006)163-168 165 Table I Properties of the as-received 3D-C/SiC Property Density Modul Poissons Porosity CTE(x10-°/C) (×103kg/m2 (GPa) MPa) ratIo 900°C1000°C1100°C1200°C 4.739 3.428 3.840 5.702 MAWp Thermal Cycle Number, N }--} tic drawing of atmosphere chamber with a detailed view of rs, the furnace and the specimen(eight major critical points 1284 dinal ends of the specimen and the oxidizing atmosphere 名 0.96 was wet oxygen including oxygen(7.90%, partial pressure Po, A8000 Pa), water vapor (14.85%0, partial pressure PH,o N 15 kPa)and argon(77.25%). The flux of gases was accurately controlled by a mass flow controller (5850 i series from BROOKS, Japan) and its precision could reach 0. 1 SCCM. Strains were measured directly from the Thermal Cycle Number, N gauge length of specimen by a contact extensometer (n- Fig. 4.(a) Strains vs. thermal cycle number N-curve for 3D-C/Sic stron model number: A1452-1001B)with a gauge length composite subjected to 50 thermal e under a constant load of 60 MPa of 10 mm b) Magnified view of the initial cycles by using logarithmic horizontal 2.3. Measurements and observations Monotonic tensile tests of the specimens after thermal cy- strains should be the coupled results of cyclic strain due cling experiments were done on the servo-hydraulic machine to thermal cycling and creep strain due to the constant (Instron 8801). The coating surfaces and fracture sections of loading(60 MPa). The contribution of the creep strain of the specimens were observed with a scanning electron the composite to the total strain is rather large at the initial microscope (SEM, JEOL JSM-6460 and HITACHI stage. Subsequently, thermal cycling becomes a dominant S-4700) factor of increasing strain. The most important informa- tion demonstrated in Fig. 4(b)is that the strain of the spec- 3. Results and discussion imen retains 0.63% under the constant load of 60 MPa at room temperature, and increases, gradually reaching a 3.1. Strain response curves of C/SiC composites subjected peak as the temperature ascends to the selected upper limit to thermal cycling and constant load of 1200C; the strain then decreases with cooling back 900C. As thermal cycling proceeds, saw-toothed strain re- Strain vS cycle number curves of the C/Sic composite peats periodically during testing and the complete period of subjected to a constant load of 60 MPa and thermal cycling each strain cycle is equal to 120 s. All the differences be- (N=50)in the wet oxygen are shown in Fig 4(a). Fig 4(b) tween the peaks and the valleys of the strain waves are is the magnified view of the initial cycles using a logarith- approximately identical in magnitude and the average mic horizontal scale. It is apparent that the measured value is about 0. 16%. Periodical thermal expansiodinal ends of the specimen and the oxidizing atmosphere was wet oxygen including oxygen (7.90%, partial pressure: P O2
8000 Pa), water vapor (14.85%, partial pressure: P H2O
15 kPa) and argon (77.25%). The flux of gases was accurately controlled by a mass flow controller (5850 i series from BROOKS, Japan) and its precision could reach 0.1 SCCM. Strains were measured directly from the gauge length of specimen by a contact extensometer (In￾stron model number: A1452-1001B) with a gauge length of 10 mm. 2.3. Measurements and observations Monotonic tensile tests of the specimens after thermal cy￾cling experiments were done on the servo-hydraulic machine (Instron 8801). The coating surfaces and fracture sections of the specimens were observed with a scanning electron microscope (SEM, JEOL JSM-6460 and HITACHI S-4700). 3. Results and discussion 3.1. Strain response curves of C/SiC composites subjected to thermal cycling and constant load Strain vs. cycle number curves of the C/SiC composite subjected to a constant load of 60 MPa and thermal cycling (N = 50) in the wet oxygen are shown in Fig. 4(a). Fig. 4(b) is the magnified view of the initial cycles using a logarith￾mic horizontal scale. It is apparent that the measured strains should be the coupled results of cyclic strain due to thermal cycling and creep strain due to the constant loading (60 MPa). The contribution of the creep strain of the composite to the total strain is rather large at the initial stage. Subsequently, thermal cycling becomes a dominant factor of increasing strain. The most important informa￾tion demonstrated in Fig. 4(b) is that the strain of the spec￾imen retains 0.63% under the constant load of 60 MPa at room temperature, and increases, gradually reaching a peak as the temperature ascends to the selected upper limit of 1200 C; the strain then decreases with cooling back to 900 C. As thermal cycling proceeds, saw-toothed strain re￾peats periodically during testing and the complete period of each strain cycle is equal to 120 s. All the differences be￾tween the peaks and the valleys of the strain waves are approximately identical in magnitude and the average value is about 0.16%. Periodical thermal expansion and Table 1 Properties of the as-received 3D-C/SiC composites Property Density (·103 kg/m3 ) Modulus (GPa) Strength (MPa) Poisson
s ratio Porosity (%) CTE (·106 /C) 900 C 1000 C 1100 C 1200 C Value 2.0 50 160 0.52 11 4.739 3.428 3.840 5.702 Fig. 3. Schematic drawing of atmosphere chamber with a detailed view of the grip holders, the furnace and the specimen (eight major critical points are indicated). Fig. 4. (a) Strains vs. thermal cycle number N-curve for 3D-C/SiC composite subjected to 50 thermal cycles under a constant load of 60 MPa. (b) Magnified view of the initial cycles by using logarithmic horizontal scale. H. Mei et al. / Scripta Materialia 54 (2006) 163–168 165