Investigation of microstructure and chemical stability in composites of NiAl reinforced by alumina-silica fibers

Interface structure and chemical stability in composites of NiAl reinforced with alumina silica fibers (Sumitomo) were investigated by means of TEM, XEDS, EELS and electron diffraction. The composite specimens were fabricated by diffusion bonding in vacuum at 1300 similar to 1450degreesC/ 5 similar to 15 MPa/2 h. The experimental results showed no Ni diffusion from the NiAl matrix into the fiber to occur during diffusion bonding. However, the fiber underwent complex thermodynamic processes depending on hot-pressing temperatures. They involved intrinsic chemical reactions between the fiber components to produce mullite and reduce silica, as well as extrinsic reactions between free oxygen and NiAl at the interface to generate alpha-A1(2)O(3). The experimental results are discussed.