Finishing PEEK Parts (Anodizing Is for Metals, Not Polymers)

No, PEEK cannot be anodized, anodizing is an electrochemical process for metals (aluminum, titanium, magnesium) that grows a protective oxide, and PEEK is a thermoplastic polymer with no metal surface to oxidize. There is no PEEK anodizing in any literal sense. PEEK is colored a completely different way: pigment is compounded into the resin before the part is molded or before the stock is extruded for machining, so color goes all the way through the material rather than being a surface layer. Standard PEEK is natural tan/beige; it's also available in black, and medical implant grades come in specific colors (PEEK-OPTIMA is often natural or other validated shades). If you need a colored PEEK part, you select a colored grade of stock, you don't apply a surface finish. If a print says anodize PEEK, it's a category error, and the real intent is either color (choose a pigmented grade), a bondable/paintable surface (plasma or chemical surface activation), or a functional coating like metallization for shielding. So the path forward is to clarify whether the requirement is appearance, adhesion, conductivity, or wear, and then pick the appropriate real process, none of which is anodizing.

PEEK is semicrystalline, and both molding and machining introduce residual internal stresses, while machining can also locally alter the crystalline structure at the surface. If those stresses aren't relieved, the part can warp, distort, or move out of tolerance over time and especially when later exposed to heat, and stressed PEEK is more prone to cracking, particularly around sharp features, threads, and thin sections. For tight-tolerance and critical PEEK parts, stress-relief annealing is therefore essentially a required finishing step: the part is heated in a controlled, staged ramp (commonly up toward 150-200°C, sometimes higher, well below the roughly 343°C melting point) and slowly cooled to relieve machining stress and stabilize dimensions and crystallinity. Best practice is often to rough machine, anneal, then finish machine, so the part is dimensionally stable at final size. If you skip annealing, the common failures are parts that drift out of tolerance after machining, warp during subsequent processing or service, or develop stress cracks, all expensive to discover late. The filled grades (glass-filled, carbon-filled) have their own thermal behavior and may need tuned schedules. For aerospace and medical PEEK where dimensional stability and reliability are non-negotiable, annealing is standard, and a reputable PEEK machining source will anneal as a matter of course and can provide the schedule used.

PEEK has an inherently low-surface-energy, chemically inert surface, which is exactly why it resists chemicals and solvents so well, but it also means adhesives, paints, and coatings will not bond to untreated PEEK; they bead up or peel. To get adhesion, the PEEK surface must first be activated to raise its surface energy and create reactive functional groups. The common methods are plasma treatment (atmospheric or low-pressure plasma, very effective and clean, widely used for medical and electronic PEEK), corona treatment, chemical etching, and abrasion/grit blasting to roughen and clean the surface mechanically. Often these are combined, for example abrade then plasma-treat. After activation, the surface energy is high enough for structural adhesives, primers, paints, or coatings to wet out and bond, and the bond should be made reasonably soon after treatment because the activation can decay over time. This surface activation is standard practice before structurally bonding PEEK aerospace and medical components, before printing or marking, and before any metallization or decorative coating. The key practical points: untreated PEEK is essentially unbondable, the activation step is what enables every downstream coating or adhesive operation, treated surfaces should be bonded promptly, and the specific method (plasma is the cleanest and most common for high-value parts) is chosen by the part value and the downstream process. None of this is anodizing, but surface activation is the polymer-world analog of the surface prep that makes coatings adhere.

PEEK is metallized when a part needs a thin metal layer on its surface for a specific function, most commonly EMI/RFI shielding on electronic enclosures and connectors, where PEEK's high-temperature performance and strength are wanted but the polymer itself doesn't block electromagnetic interference, so a conductive metal coating is applied. Other reasons include decorative metallic finishes, reflective or optical surfaces, and certain electrical-contact or sensor applications. Metallization is done by vacuum processes like sputtering or evaporation (depositing a thin metal film such as aluminum, copper, gold, or nickel in a vacuum chamber) or by electroless/electroplating after the surface is activated and seeded. The critical enabler is surface preparation: because PEEK is chemically inert and low-energy, the surface must be activated (plasma, etch, or abrasion) and often given an adhesion-promoting base layer so the metal film bonds durably rather than flaking off. Sputtered films are thin (typically sub-micron to a few microns) and conformal, good for shielding and decorative work; plated builds can be thicker for more robust conductivity. A useful related point: carbon-fiber-filled PEEK is partially electrically conductive on its own and is often used directly for static dissipation in semiconductor wafer-handling and ESD-sensitive parts, which can avoid the need for metallization in those applications. So metallize PEEK when you need surface conductivity, shielding, reflectivity, or a metallic look on a high-performance polymer part, do it by vacuum deposition or plating over a properly activated surface, and consider carbon-filled grades when only static dissipation is required.