CONTINUOUS CARBON FIBER NICKEL ALUMINIDE COMPOSITES.

This metal matrix composite consists of continuous carbon fiber in a nickel aluminide matrix. It is made by first coating a tow of carbon fiber with nickel, then coating the nickel-coated carbon fiber with aluminum by CVD from an organo-metallic precursor. By using a CVD process, each of the 12 thousand fibers in the tow can be evenly coated with both nickel and aluminum. The carbon fiber is typically 7 microns in diameter and the nickel and aluminum coating are typically1 micron each. A fractured filament of the carbon fiber coated with both nickel and carbon is shown in Figure 1. In this state the fibers are still loose and drapable and are analogous to conventional composite prepreg. The loose fiber bundles or tows are then laid up in a graphite die and compressed in vacuum at temperatures up 1200°C. The nickel and aluminum react exothermically to form an inter-metallic compound called nickel aluminide. Nickel aluminide is the strengthening phase in most high temperature superalloys. It is oxidation resistant and is thermodynamically stable with respect to the carbon fiber. The thickness of the nickel and aluminum coating is controlled so that the volume percent carbon fiber in the resulting composite is around 50 % and the composition of the matrix can be from NiAl to Ni3Al. A metal matrix composite is formed with a strength of around 800 MPa and a modulus of 115 GPa with a density of around 3.9 g/cc. A fracture surface of the composite is shown in Figure 2. Note the uniform distribution of the carbon fiber and the lack of reaction with the matrix. This composite has the highest specific strength of any aerospace material in the 400 to 700°C temperature range.

This material is protected by US patent 5,967,400.