SCS-6 SiC fiber

Fig. 7.23. Thermal residual stress distributions in the (a) radial, (b) circumferential and (c) axial directions for a SCS-6 SiC fiber/TisAI + Nb matrix composite with and without Cu, Nb and Cu/Nb coatings. Total coating thickness t/a = 0,1. After Arnold and Wilt (1992).

Fig. 5.2 Comparison of creep behavior and time-dependent change in fiber and matrix stress predicted using a 1-D concentric cylinder model (ROM model) (solid lines) and a 2-D finite element analysis (dashed lines). In both approaches it was assumed that a unidirectional creep specimen was instantaneously loaded parallel to the fibers to a constant creep stress. The analyses, which assumed a creep temperature of 1200°C, were conducted assuming 40 vol.% SCS-6 SiC fibers in a hot-pressed SijN4 matrix. The constituents were assumed to undergo steady-state creep only, with perfect interfacial bonding. For the FEM analysis, Poisson s ratio was 0.17 for the fibers and 0.27 for the matrix, (a) Total composite strain (axial), (b) composite creep rate, and (c) transient redistribution in axial stress in the fibers and matrix (the initial loading transient has been ignored). Although the fibers and matrix were assumed to exhibit only steady-state creep behavior, the transient redistribution in stress gives rise to the transient creep response shown in parts (a) and (b). After Wu et al 1...

Textron s SCS-6 SiC fiber was ineluded in Table 3-1 primarily because if has excellenf room-temperature strength and creep-rupture resistance. It is currently made in monofilament form, but multifilament tow fabrication is being researched. The excellent mechanical properties of this fiber apparently arise from its uniform, fine grained ( 0.04 to 0.1 pm [0.002 to 0.004 mils]) microstructure and its single-phase stoichiometric p-SiC composition. 

Properties SiC (SCS-6) monotilament SiC (Niealon) liber Boron (B W) fiber ... 

There are four types of SCS fibers depending on the thickness of the final SiC coating designed for different metal matrices. They are the standard SCS, SCS-2, SCS-6 and SCS-8. Fig. 5.30 illustrates schematically the cross sections of two commercially produced SiC fibers, the standard SCS and SCS-6 fibers, according to DiCarlo (1988). Both types of fibers consist of a carbon core of 37 pm in diameter, a SiC sheath of varying thickness and a carbon-rich surface coating of 0-4 pm in... 

Additional surface modifications on vapor deposited SiC fibers, including WC. TaC, TiN, B4C, Al, Ni and Fe, have been applied with varying degree of success (Wawner and Nutt, 1980 DeBolt, 1982 Wawner, 1988). After exhaustive trial and error, TiB is selected as an additional coating material to further prevent the diffusion-induced reactions between the SCS-6 fibers and matrix materials, including Ti alloys and Ti Al intermetallic alloys (e.g. Ti Al, TiAl and TiAl ) (Donncllan and Frazier, 1991 James et al., 1991). When the coated fiber is subjected to tensile... 

Fig. 2.7 The tensile stress-strain curves versus temperatures for (a) unidirectional SCS-6 fiber-reinforced hot-pressed Si3N4, (b) unidirectional SCS-6 fiber-reinforced reaction-bonded Si3N4, (c) 2-D Nicalon fabric-reinforced CVI-SiC, and (d) 3-D braided Nicalon fabric-reinforced CVI-SiC.49-52...

Fabrication by Liquid Silicon Infiltration (reaction bonding) (LSI) A leading candidate for use in industrial gas turbine engine is a SiC matrix composite named toughened Silcomp [175]. It is produced by melt infiltration of molten silicon into a porous preform containing carbon as well as BN-coated SiC fibers (e.g. Textron SCS - 6). The composites thus produced consist of a fully dense matrix of SiC + Si, reinforced with continuous SiC fibers. Moreover, the melt infiltration process is net shape and fast. Ultimate strength and strain at ultimate strength are 220 MPa and 0.8 /o, respectively at room temperature (LSI-SiC/SiC Si). 

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