3D-printed polymers can create lightweight, complex parts with remarkable design freedom, but their surfaces often remain a weak link. Rough finishes, limited wear resistance, and poor adhesion to protective coatings can restrict their use in demanding applications. Now, researchers have demonstrated that carefully engineered metal and ceramic multilayer coatings can overcome these limitations, giving commonly used polymers tougher, more durable surfaces.
Study: Enhancing surface properties of 3D printed polymers by metal and ceramic multilayer coatings. Image Credit: MarinaGrigorivna/Shutterstock.com
Published in Results in Surfaces and Interfaces, the study focuses on polyurethane (PU), polypropylene (PP), and polyamide (PA), materials that have received comparatively little attention in coating research. By tailoring the layers between the polymer and its protective surface, the researchers achieved strong adhesion and impressive wear resistance, pointing to a practical route for producing longer-lasting, functionally enhanced 3D-printed components.
Overcoming Surface Limitations in 3D-Printed Polymers
Additive manufacturing has evolved from a rapid-prototyping method into an established manufacturing technology. Polymer 3D printing is especially attractive because it produces lightweight, complex components directly from digital designs. However, surface quality remains a significant limitation, particularly for parts made by fused filament fabrication (FFF).
Layer-by-layer deposition often creates rough surfaces with visible printing features. Removing support structures can further damage or unevenly alter the surface. These limitations may prevent manufacturers from using printed components directly in applications that require good appearance, durability, or functional performance.
Surface coatings offer a way to address these challenges. Metallic and ceramic layers can provide properties the polymer alone cannot, including greater wear resistance, corrosion protection, surface hardness, and electrical functionality. However, polymers present difficult coating substrates because metals and ceramics often adhere poorly to them.
Conventional plating on plastics may also require several surface-preparation steps and hazardous chemicals. To address these concerns, the researchers explored simpler and potentially more environmentally friendly methods for creating strong adhesive interfaces.
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Engineering Adhesive Multilayer Coatings
The researchers developed several coating strategies to improve the interface between each polymer substrate and its final metallic or ceramic layer. They tested both 3D-printed specimens and reference specimens made from the same polymers. This comparison allowed them to assess coating performance across different substrate conditions.
The researchers applied intermediate layers by brushing, providing a relatively simple surface-treatment method. They also used ultra-short, pulsed laser deposition (USPLD) to produce thin intermediate films. This vapor-deposition technique remains relatively underused for polymer surface modification, but it offers considerable flexibility.
The team evaluated the multilayer systems through mechanical and tribological testing. Scratch tests measured the loads required to initiate coating damage and cause complete failure. Pull-off tests quantified the adhesion strength between each coating system and its polymer substrate.
The researchers assessed wear resistance with pin-on-disk tests under a 300 g load. The coatings underwent up to 12,000 cycles, corresponding to a sliding distance of approximately 377 m. Together, these tests provided a detailed assessment of adhesion, mechanical integrity, and resistance to repeated sliding contact.
Multilayer Coatings Improve Adhesion and Wear Resistance
Coating performance varied significantly by polymer substrate, intermediate layer, and final coating. Mechanical testing showed that no single coating system performed best across all substrates and test methods.
Among the ceramic coatings, enamel paint consistently outperformed enamel spray, especially in scratch adhesion and wear resistance. More than half of the enamel paint coatings withstood loads above 30 N before total scratch failure, whereas none of the enamel spray coatings reached this level.
The metallic coating systems also performed well, although their performance depended strongly on the substrate. Electrochemical Cu + Ni coatings with a conductive silver intermediate layer performed particularly well on PP sheet and 3D-printed smooth PA. Cu + Ni + Cr coatings with a USPLD Ti + Ni intermediate layer performed strongly on PP sheet, PA sheet, and 3D-printed rough PA.
Among the best-performing metal systems, scratch resistance exceeded 35 N before total failure, while pull-off adhesion reached approximately 8–15 MPa. Coatings with conductive silver intermediate layers performed well when they were more uniformly coated across the different substrates, whereas USPLD-based systems showed greater variation depending on the polymer surface.
Wear testing further confirmed the durability of the metallic coatings. Both conductive-silver and USPLD-based metal coatings completed the pin-on-disk tests without wearing through, despite differences in their top electroplated layers. These results indicate that the successful metallic systems provided consistently strong wear resistance, while scratch and pull-off performance depended more strongly on the specific polymer–intermediate-layer–coating combination.
Among the ceramic systems, enamel paint performed effectively on 3D-printed PUR and PP, PA sheet, and 3D-printed rough PA, while enamel spray performed well on 3D-printed rough PP. Overall, the study demonstrated that each coating performed well on at least one substrate and that every polymer substrate accepted at least one successful coating.
Expanding the Functional Potential of Additive Manufacturing
The study shows that the limitations of 3D-printed polymers do not necessarily end with the printing process. With the right surface treatment, materials such as PU, PP, and PA can gain the tougher, more wear-resistant surfaces needed for more demanding uses.
Importantly, no universal coating solution existed. Performance depended on the polymer, the intermediate layer, and the final coating. Enamel paint stood out among the ceramic options, while conductive silver and USPLD-based intermediate layers produced durable metallic coatings on several tested substrates.
The approach could also offer a cleaner alternative to conventional plastic-coating methods. The researchers achieved strong adhesion using relatively simple intermediate layers and USPLD, avoiding some of the hazardous chemical pretreatments and lengthy processing steps traditionally associated with coating polymers.
There is still room to refine the process, from adjusting USPLD parameters to tailoring coating structures for particular materials and applications. But the results suggest that surface engineering could help move 3D-printed polymers into roles where lightweight, complex parts must also withstand the wear and tear of everyday use.
Journal Reference
Laitinen, K., Korhonen, H., et al. (2026). Enhancing surface properties of 3D printed polymers by metal and ceramic multilayer coatings. Results in Surfaces and Interfaces, 25, 100951. DOI: 10.1016/j.rsurfi.2026.100951. https://www.sciencedirect.com/science/article/pii/S2666845926002436
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