Mechanical and microstructural evolution of Hi-Nicalon trade mark SiC fibers annealed in O-2-H2O-Ar atmospheres
Mei, Hui（ NW Polytech Univ, Natl Key Lab Thermostruct Composite Mat）
Zhang, Litong（ NW Polytech Univ, Natl Key Lab Thermostruct Composite Mat）
- 化学化工－已发表论文 
Hi-Nicalon fibers were exposed in 8% O-2/78% Ar/14% H2O atmosphere for 1 h at 1300, 1400, 1500, 1600 degrees C, respectively. Residual tensile strength was evaluated by tensile test, phases in the fibers were identified using an X-ray diffractometer (XRD), morphology of the fracture surfaces and microstructure was observed by scanning electron microscope (SEM) and transmission electron microscope (TEM), respectively. Results indicated that residual tensile strength increased with increasing temperature from 1300 to 1500 degrees C, then decreased after annealing in 1600 degrees C. The grain size of beta-SiC and the amount of the stacking faults increased under the elevated temperature as well. After annealing, a passive film with a structure of alpha-cristobalite crystals dispersed in amorphous SiO2 phase formed on the fiber surface, the thickness of the film increased with the annealing temperature from 1300 to 1500 degrees C, after annealing in 1600 degrees C, fractional silica film spalled. Finally, relationship between the structural changes and the mechanical properties, the control effect of water vapor on formation and structural evolution of the passive film were discussed. (c) 2007 Elsevier B.V. All rights reserved.