Diamond-like carbon coatings for improved mechanical performance of polymer materials

• Main Author: Carley, Sean Michael
• Other Authors: Neville, Anne
• Published: University of Leeds 2017
• Subjects: 620.1
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.725012

The use of polymers has become more widespread over recent decades as an important material for light-weighting components across many industries. As the most efficient use of oil, they allow complex geometries to be manufactured, with lower weight than metallic or alloy counterparts, whilst remaining low cost. As the use of polymers continues to increase, so does the drive towards lightweight components required for increased efficiency in many industries. Therefore, the need for engineering polymers to be useful in a wider range of applications has become a necessity. In this study, the use of Microwave assisted Plasma Enhanced Chemical Vapour Deposition (MW-PECVD) has been investigated as a way to deposit Diamond-Like Carbon (DLC) coatings directly onto polymer substrates. A Design of Experiments (DOE) approach was used to characterise the process with respect to how deposition parameters changed the mechanical properties of the coatings. A Hauzer Flexicoat 850 deposition system, at the University of Leeds, was used to deposit 10 unique DLC coatings onto ABS and PEI polymers using a novel MW-PECVD technique. These coatings were then characterised to quantify their hardness, Young’s modulus, thickness, chemical and structural composition. Further coatings were produced to explore the limitations of characterisation techniques for hard-on-soft coating systems. Scratch testing, cross hatch tests, and contact angle goniometry were used to assess coating adhesion, and reciprocating pin-on-plate tests were used to assess tribological properties. This study has shown that the MW-PECVD technique is able to deposit strongly adhered hydrogenated amorphous carbon (a-C:H) coatings onto polymer substrates at high deposition rates, without damaging the thermally sensitive material. The coatings demonstrated the ability to increase the hardness and Young’s modulus of the surface, however substrate effects are still present at ultra-low depth indentations of < 5% of coating thickness. These substrate effects show the limitation of the system to withstand practical loads, and the measurements of P/S2 (a measure of resistance to plastic deformation) allowed visualisation of coating strain to failure and was the only measurement that could reliably distinguish between substrates with differing mechanical properties.