Polymeric Matrix Composites, especially Carbon Fiber Reinforced Polymers (CFRP) laminates, are innovative materials used for advanced engineering applications where the structural design is driven by high strength-to-weight and high stiffness-to-weight ratio requirements.
However, because of structural distortions induced by moisture absorption effects, polymeric matrix composites are not suitable for high precision machines/equipment where long-term geometrical stability is required. In order to improve the hygroscopic properties of these materials, amorphous silicon-like films (a-Si:Ox:Cy:Hz:) produced by Plasma Enhanced Chemical Vapour Deposition (PECVD) from a mixture of hexamethyldisiloxane (HMDSO), O2 and Ar have been deposited on their surface. A barrier film against moisture was deposited in conditions of high monomer (HMDSO) fragmentation. To prevent the absorption of cutting fluids during machining operations, a more superficial thinner layer was grown in conditions of low monomer fragmentation so that the film acquires hydrophobic properties. Different hydrophobic layers were grown to choose the one which best fulfil hydrophobicity, evaluated by both water contact angles measurements, and wear-scratch resistance. The films so obtained are hybrid because they are deposited with changed parameters during the plasma process. The infrared spectroscopic analysis shows these hybrid films do not absorb water vapour during the time, while the same analysis made on conventional protection coatings (e.g. polyurethane coatings) reveals moisture absorption. Micro-mechanical tests (using a micro-tribometer) were carried out to characterize the wear-scratch behaviour of the films. The number of cycles to wear under a given normal force is measured and compared for different surface coatings. SEM images show a good adhesion of the film to the composite substrate.
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