Characterisation of thin silica films deposited on carbon fibre by an atmospheric pressure non-equilibrium plasma (APNEP)

Low modulus carbon fibres were used to investigate the potential of a low cost novel atmospheric pressure microwave plasma technique for continuously depositing silica coatings onto carbon fibres, in a tow form. The objective was to improve the interfacial properties of aluminium/carbon fibre composites produced by liquid metal infiltration techniques. Amorphous silica coatings, approximately 50–400nm thick, were successfully produced in a continuous process. The nature and morphology of the coatings were determined using transmission electron microscopy. Squeeze cast and gas pressure infiltrated samples were manufactured to investigate the fibre/matrix interface using tensile tests and a short beam interlaminar shear test. The tensile samples displayed brittle fracture with ultimate tensile stresses of 223 and 251MPa for the uncoated and coated fibres, respectively. The shear samples did not show any interlaminar shear, but failed in tension. It is concluded that the silica coating did not have a significant effect on improving the carbon fibre/aluminium matrix interface. However, the microwave plasma technique was very successful and can be modified to produce low cost alternative coatings for future development.