Nextel fibers

FIGURE 4-7 Nextel 610 fiber showing small grain size resulting from the addition of nucleation agents. Source 3M Company. 

Many layered oxide coatings show promise as crack deflecting interfaces for oxide-oxide composites. Although the jl-aluminas have been shown to be unstable with Nextel 720 fibers, they are still candidate fiber coatings (especially the less volatile RbAlnOiy) for ceramic composites if other creep-resistant oxide fibers become available. Research into an improved creep-resistant Nextel 610 fiber that incorporates additions of rare-earth oxides or garnet-based fibers, may make the (5-... 

Other manufacturers have modified the production technique to reduce the diameter of the alpha-alumina fibers that they have produced. This reduction of diameter has an immediate advantage of increasing the flexibility and hence the weaveability of the fibers. Mitsui Mining and 3M Corporation have introduced polycrystalline fibers, the Almax and the Nextel 610 fibers with diameters of 10 p.m, that is half the diameter of Fiber FP. 

Figure 7 compares the creep behavior of the three nearly pure a-alumina fibers. It can be seen that Fiber FP crept at the lowest rate at each temperature. The smaller grains in the Nextel 610 fibers allowed them to creep faster whilst the porosity and residual stresses in the Almax fibers meant that they crept the fastest (23). 

Almax and Nextel 610 fiber-reinforced composite samples were exposed to 1000°C in air for 100 h and then tested in four point flexure. At least 80% of the as-fabricated... 

A.S. Fareed and G.H. Schiroky, Microstructure and Properties of Nextel 610 Fiber Reinforced Ceramic and Metal Matrix Composites, Ceram Eng. Sci. Proc., 15 [4] 344-352( 1994). 

Selected composite materials and their basic physical properties are summarized in Table 2. The GE GEN-IV all-oxide fiber composites have a relatively low volume fraction (30%) of Nextel 610 fiber and a matrix composed of alumina and silica with approximately 35% porosity [12, 30, 37]. COI produces a number of aluminosilicate matrix materials with a selection of different Nextel oxide fibers, but with higher fiber loading and matrix porosity than the GE materials [140, 141]. Two examples of nominally silica-free porous composites (Table 2) with improved thermal stabilities are the mullite-alumina formulation developed at UCSB [4,44,142,143] and the all-alumina COI N720/A-1 [75, 79, 141, 144],... 

FIGURE 12. Air permeability of different WHIPOX CMCs consisting of Nextel 610 fibers and Al203/mullite... 

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