Metallic Coating Production on Polymer-Matrix Composites

Polymer-matrix composites (PMC) based on continuous carbon fibres (CF) are increasingly used in aerospace applications where the majority of PMC parts are made from high fibre volume fraction (vf) continuous fibre carbon/epoxy systems. It is envisioned that thin coatings made of selected metallic materials could increase erosion and sliding wear protection in airframes with minimal extra weight. It is also envisioned that thermal management in parts or heat conduction in PMC moulds used in out-of-autoclave processes could be addressed by thin metallic coatings. Despite their large successes in many applications, it has been shown that thermal spray processes are not best suited to coat such parts and moulds and limited success has been achieved only using multiple operations and coats.

 This paper demonstrates a method for applying thin metallic coatings (few hundreds of microns) on high vf, continuous fibre carbon/epoxy PMCs. No surface preparation or modification was used hence no damage was induced in brittle carbon fibres prior to coating application. The coatings were produced using the Pulsed-Gas Dynamic Spraying (P-GDS) process to deposit metallic feedstock particles on PMC laminates. Low powder and gas temperatures were used to avoid degrading the epoxy and damaging the carbon fibres. Dense coatings were obtained with minimal substrate heating thus eliminating substrate damage. The effect of the process and the feedstock powder on the coating microstructure and composite material (substrate) are investigated using optical microscopy (OM) and micro-hardness measurements.