There are different types of carbon fiber composite materials: carbon carbon composite material, carbon ceramics composite material, carbon fiber reinforced metal composite, Carbon fiber reinforced ceramics, glass and cement…
Carbon fibers were successfully incorporated in ceramic and glass matrices, and some people had provided a good review of carbon fiber reinforced cement.
Carbon fiber reinforced metal composites.
A section within Harwell investigated carbon fiber/metal composite and looked at:
- Coating carbon fibers with metal and producing a composite by hot compaction.
The metal was deposited by electro and electroless plating, vacuum deposition and deposition by the decomposition of organometallic compounds.
Electroplating was the preferred method and copper was successfully plated at 3 m/h onto a 10 k tow using a formulated cyanide bath (CuCN, NaCN, Na2CO3) and, although giving a porous and slightly uneven product, gave a satisfactory 30% Vf composite after hot pressing, but as the fiber volume fraction increased the strength deteriorated. Nickel was also successfully plated onto a Type 2 untreated carbon fiber using either a Watt’s bath or a sulfamate bath, which produced a brittle plate but made a good composite after compaction.
Copper and Nickel were successfully coated using electroless plating techniques to give excellent penetration of the tows with a uniform deposit, but the method proved to be too expensive.
Barrel plating could be used for applying Sn, Pb and Ni. Although the deposits were uniform, the plate tended be powdery with only moderate adhesion and when hot pressed, contained above average values of oxide.
Vacuum deposition was not successful due to shadowing, with resultant poor penetration of the tow bundle.
Good coating were obtained by the thermal decomposition of tri-isobutyl aluminum but, when hot pressed, some debonding occurred, showing an improvement when isostatic cold pressing was used.
Two techniques were used for hot pressing; on where the coated fiber was placed in a graphite or tool steel die, heated in an electric furnace, or an RF heater, and consolidated by compression in a hydraulic press; and the other involved isostatic pressing, ensuring an even distribution of pressure over the work piece, by packing the coated fiber in a sealed silicone bag, immersing in oil in a pressure chamber, heating if required and finally applying pressure. This technique worked well with less than 1% break-up of fiber and gave good consolidation with only slight porosity. As a rule to minimize fiber break-up, it was found beneficial to use as high a temperature and as low pressure as possible.
- Hot working a mixture of metal powders and chopped carbon fiber
This technique was evaluated for 10um nominal diameter aluminum powder. Attempting to dry mix with the chopped fiber proved difficult. Eventually a binder was used that had sufficient tack, once the solvent had evaporated, to hold the aluminum powder to the fry fiber. The mix was then packed into aluminum cans and the binder removed by baking in vacuo. The cans were evacuated, sealed by electron beam welding and extruded at 600-625C giving extrusions containing 8-25% Vf. Some of the samples were annealed for 1.5h at 500C and, although results were below those predicted by the law of mixtures, they were of the same order.
- Liquid metal infiltration techniques.
When using liquid metal infiltration techniques, it was found preferable to initially apply a thin plating coat of copper to the carbon fiber in order to give improved infiltration. The coated fiber was gathered into a bundle and packed into an open silica tube, which was then immersed into the molten matrix alloy, the process being carried out in vacuum with an 8-12% volume fraction of carbon fiber being achieved. A modification of the matrix to produce a wetting but not strongly reacting system is described by Nicholas and Mortimer. this is what we call metal matrix composites.