Enhancing additively manufactured polymers through functional diamond-like carbon coatings

By providing the required structural modification to polymeric materials through functional coatings, polymer-based materials (PBMs) can provide significant material functionality and improve performance in both material design and product finishing. This added advantage may provide extended durability, aesthetic appeal, barrier functions and improve tribological performance to the polymer. PBMs especially additively manufactured polymers (3D printed polymers) come with enormous physical, structural, mechanical and chemical challenges in both design and product application phases and can only be mitigated using an integrated surface engineering approach. In this study, the use of a novel microwave-plasma-enhanced chemical vapour deposition (MW-PECVD) technique has been assessed for its viability in depositing single layer diamond-like carbon (DLC) coatings directly unto 3D printed polymers. Before the deposition, a comprehensive assessment to understand the performance limitations of the mechanical, thermal, pore structure and water absorption properties of all selected 3D printed parts were made. The Hauzer Flexicoat 850 system which houses within two microwave sources was utilized in the DLC deposition process to offer a uniquely designed and tailored coating structure. Three DLC coatings were developed and deposited onto two photocurable additively manufactured polymers namely acrylonitrile butadiene styrene-like (3D ABS) and Verogray. The parameters of particular interest for the deposition process including N_2,〖 C〗_2 H_2 gas flow rates and micro-wave power input were studied to determine the effect these process variations have on the coating architecture, structure and performance from the nano to the macro scale. Initial adhesion testing of the coating using scratch testing showed complete coating failure at loads < 5N. A preliminary design of experiment (DOE) approach was established as a base framework to understand the relationship between the process parameters and coating adhesion. Further coatings based on this design were produced to explore the variable applications and limitations for characterising the hard-on-soft polymer-coating matrix. Coating characterisation techniques such as scratch testing, nano-indentation, Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) were employed to assess both the mechanical and structural properties of the coating. The coating produced in this work has shown measurable mechanical and structural properties, in particular high hardness and improved adhesion in comparison with similar DLCs reported in the literature. The ability of the coating to provide additional functionality such as tribological and water vapour barrier functions is assessed in this work. This study has shown that it is viable to use DLC for both barrier and tribological applications.