TEM of grain growth and phase transformations during creep of SCS-6 silicon carbide fibers

The SCS-6 SiC fiber is a 142 μm diameter fiber consisting of four distinct regions of βSiC. These SiC regions vary in excess carbon content ranging from 10 a/o down to 5 a/o in the SiC1 through SiC3 region. The SiC4 region is stoichiometric. The SiC sub-grains in all regions grow radially outward from the carbon core of the fiber during the chemical vapor deposition processing of these fibers. In general, the sub-grain width changes from 50nm to 250nm while maintaining an aspect ratio of ~10:1 from the SiC1 through the SiC4 regions. In addition, the SiC shows a <110> texture, i.e., the {111} planes lie ±15° along the fiber axes. Previous has shown that the SCS-6 fiber (as well as the SCS-9 and the developmental SCS-50 μm fiber) undergoes primary creep (i.e., the creep rate constantly decreases as a function of time) throughout the lifetime of the creep test.

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The Effect of Excess Carbon on the Crystallographic, Microstructural, and Mechanical Properties of CVD Silicon Carbide Fibers

MRS Proceedings ◽

10.1557/proc-0982-kk07-16 ◽

2006 ◽

Vol 982 ◽

Cited By ~ 1

Author(s):

James V Marzik ◽

William J. Croft ◽

Richard J. Staples ◽

Warren J. MoberlyChan

Keyword(s):

Electron Microscopy ◽

Mechanical Properties ◽

Silicon Carbide ◽

Elastic Modulus ◽

Chemical Vapor ◽

High Strength ◽

Excess Carbon ◽

X Ray ◽

Silicon Carbide Fibers ◽

Sic Fiber

ABSTRACTSilicon carbide (SiC) fibers made by chemical vapor deposition (CVD) are of interest for organic, ceramic, and metal matrix composite materials due their high strength, high elastic modulus, and retention of mechanical properties at elevated processing and operating temperatures. The properties of SCS-6™ silicon carbide fibers, which are made by a commercial process and consist largely of stoichiometric SiC, were compared with an experimental carbon-rich CVD SiC fiber, to which excess carbon was added during the CVD process. The concentration, homogeneity, and distribution of carbon were measured using energy dispersive x-ray spectroscopy (SEM/EDS). The effect of excess carbon on the tensile strength, elastic modulus, and the crystallographic and microstructural properties of CVD silicon carbide fibers was investigated using tensile testing, x-ray diffraction, scanning electron microscopy (SEM), and transmission electron microscopy (TEM).

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Application of chemical vapor deposited yttria for the protection of silicon carbide fibers in a SiC/Ni3Al composite

Journal of Materials Research ◽

10.1557/jmr.1990.2706 ◽

1990 ◽

Vol 5 (11) ◽

pp. 2706-2717 ◽

Cited By ~ 15

Author(s):

D. J. Larkin ◽

L. V. Interrante ◽

A. Bose

Keyword(s):

Silicon Carbide ◽

Nickel Aluminide ◽

Chemical Vapor ◽

Degradation Process ◽

Auger Spectroscopy ◽

Silicon Carbide Fibers ◽

Sic Fiber ◽

Chemical Vapor Deposited ◽

Volatile Products ◽

Before And After

A CVD process has been developed for coating Textron-Avco SCS-6 SiC fiber with yttria. Both Y(fod)3·H2O and Y(thd)3 (fod = 1,1,1,2,2,3,3-heptafluoro-7,7-dimethyl-4,6-octanedionato; thd = 2,2,6,6-tetramethyl-3,5-heptanedionato) were examined as potential Y2O3 CVD precursors. Analysis of the deposits by Auger spectroscopy indicated significant F and C'incorporation in the case of Y(fod)3 · H2O whereas, under appropriate conditions, Y(thd)3 gave a deposit which was essentially free of C and other impurities. GCFTIR analysis of the volatile products of the CVD process indicated isobutylene, tetrafluoroethylene, 1,1-difluoroethylene, fluoroform, and fluoroethylene for Y(fod)3 · H2O and mainly isobutylene and propylene for Y(thd)3. The precursor Y(thd)3 was chosen to deposit 1–2 μm of yttria on short lengths of silicon carbide fibers. The coated fibers were then incorporated into a nickel aluminide (Ni3Al) matrix by reactive sintering, with yttria affording protection from the known SiC + 2Ni ⇉ Ni2Si + C degradation process. The SiC/Ni3Al composites, before and after annealing at 1000 °C for up to 100 h, were studied by using SEM and EMPA to determine the extent of reaction. With the exception of certain portions of the fibers that were inadequately coated with yttria, complete protection of the fibers was indicated.

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Multifilament Silicon Carbide Fibers by Chemical Vapor Deposition (CVD)

High Temperature Materials and Processes ◽

10.1515/htmp.1991.10.1.55 ◽

1991 ◽

Vol 10 (1) ◽

pp. 55-65 ◽

Cited By ~ 1

Author(s):

Vithal V.S. Revankar, ◽

Vladimir Hlavacek,

Keyword(s):

Silicon Carbide ◽

Chemical Vapor Deposition ◽

Vapor Deposition ◽

Chemical Vapor ◽

Silicon Carbide Fibers

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Light Ion Irradiation Creep of SCS-6 Silicon Carbide Fibers in the Temperature Range 450 – 1100°C

MRS Proceedings ◽

10.1557/proc-540-279 ◽

1998 ◽

Vol 540 ◽

Author(s):

R. Scholz ◽

H. Pasic

Keyword(s):

Silicon Carbide ◽

Creep Rate ◽

Ion Irradiation ◽

Chemical Vapor ◽

Chemical Vapor Infiltration ◽

Irradiation Creep ◽

Creep Tests ◽

Temperature Range ◽

Silicon Carbide Fibers ◽

Light Ions

AbstractCreep tests were conducted in torsion on Textron SCS-6™ silicon carbide (SiC) fibers during irradiation with light ions in the temperature range 450-1100°C up to doses of 0.06 dpa. The fibers, produced by chemical vapor deposition (CVD), should be representative of a SiC/SiC composite matrix produced by chemical vapor infiltration (CVI).For temperatures between 450 and 600°C, the irradiation creep curves were characterised by long lasting strain transients during which the creep rate slowed down before reaching approximately steady state values. On a decrease in temperature the creep rate increased.For temperatures between 900 and 1100°C, the transient creep regime was negligible. The creep rates reached constant values shortly after starting the irradiation and increased with temperature. The activation energy was E = 0.55±0.15 eV.The results are discussed in terms of concentration and mobility of point defects and the change of these quantities with temperature.

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