Sylramic fiber

High temperature thermal exposure in argon shows very little affect on the room-temperature strength of the Dow Coming Sylramic fiber or the Carborundum fiber. Figure 3-8 shows the effect of thermal aging on the room-temperature strength of Sylramic fiber in comparison to other polymer-derived fibers. 

Table 1 lists some key production and compositional details for a variety of SiC-based fiber types of current interest and availability as CMC reinforcement. The polymer-derived types range from first-generation fibers with very high percentages of oxygen and excess carbon, such as Nicalon and Tyranno Lox M, to the more recent near-stoichiometric (atomic C/Si 1) fibers, such as Tyraimo SA and Sylramic. For the CVD-derived types, such as the SCS family with carbon cores, the only compositional variables in the SiC sheaths are slight excesses of free sihcon or free carbon. Table 2 lists some of the key physical and mechanical properties of the SiC fiber types in their as-produced condition, as well as estimated commercial cost per kilogram, all properties important to fiber application as CMC reinforcement. These SiC fiber properties in Tables 1 and 2 are in most part those published by the indicated commercial vendors. It should be noted that the Sylramic fiber... 

For the N24-A system, these issues surrounding the as-produced Sylramic fiber and its sizing were first overcome by using Sylramic fibers with an alternate Sizing B that yielded much less carbon char than Sizing A. In addition, NASA developed a thermal treatment in... 

The three major constituents of any continuous fiber ceramic matrix composite are the reinforcing fibers, the matrix and a fiber-matrix interphase, usually included as a coating on the fibers. HiPerCompTM composites can be processed with various monofilament and multifilament fibers, such as the SCS family of monofilament SiC from Specialty Materials, Inc. CG-Nicalon and Hi-Nicalon Type S from Nippon Carbon Company Tyranno ZE , Tyranno ZMl and Tyranno S A from Ube Industries and Sylramic fiber from COl Ceramics. However, the composites described in this paper all utilize Hi-Nicalon SiC fiber from Nippon Carbon Company. A companion paper, in this book, by Jim DiCarlo [11] from NASA gives the properties of slurry cast composites reinforced with Sylramic and Sylramic-iBN fibers. 

Melt Infiltrated In-Situ BN SiC/SiC composite (MI SiC/SiC) is the material that was documented in the past work (5). The MI SiC/SiC system has a stochiometric SiC (Sylramic ) fiber in a multiphase matrix of SiC deposited by chemical vapor deposition followed by slurry casting of SiC particulates with a final melt infiltration of Si, The specific MI SiC/SiC tested had 36% volume fraction fibers using a 5 HS weave at 20 EPI with a cross ply lay-up. A cross section of the material is shown in Figure 1. 

The Sylramic fiber was fabricated by DuPont as a 10 pm diameter stochiometric SiC fiber and bundled into tows of 800 fibers each. The sizing applied was polyvinyl alcohol (PVA). For this study, the four lots of fibers, which were used, were wound on 19 different spools. The tow spools were then woven into a 5 harness satin (HS) balanced weave at 20 ends per inch (EPI). 

Sylramic fiber (by Dow Corning) is an SiC fiber containing a small amount of TiB2 and B4C, and produced using polytitanocarbosilane precursors containing a small amount of titanium [33]. 

The eomposites used in this study were described in detail elsewhere [1-2). The Ml SiC/SiC composite was fabricated by GE Power System Composites. Briefly, Sylramic fibers, produced in tow form by Dow Coming (Midland, MI) were woven into 2-D 5 harness-satin cloth and then converted to Sylramic iBN fibers. The Sylramic iBN cloth was cut into a pertinent size, which was 0/90°, 8 ply-stacked and chemically vapor infiltrated with a thin BN-based interface coating followed by Sic matrix over-coating. Remaining matrix porosity was filled with SiC particulates and then with molten silicon at I400°C. The composite was composed of about 34 vol% SiC fibers. The nominal dimensions of each panel thus fabricated were about 230 mm by ISO mm with a thickness of about 2.2 mm. 

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