Atomic layer deposition of oxide coatings on porous metal and polymer structures fabricated by additive manufacturing methods (laser-based powder bed fusion, material extrusion, material jetting)

Complex porous 316 L stainless steel, Ti-6Al-4V, Ti-6Al-7Nb, ULTEM™ 1010 and MED610™ polymer structures were produced with additive manufacturing methods. The structures were surface functionalized by atomic layer deposition of titanium, zinc and zirconium oxide coatings with a thickness between 14 and 43 nm. Deep and narrow structures with aspect ratios >10 could be coated. Titanium oxide films are mostly amorphous when plasma-assisted deposition is used and contain nanocrystalline anatase when deposited by thermal atomic layer deposition. The deposited titanium oxide grains ranged in size from ∼20 to 60 nm. In interior parts of the fractured porous polymer model structures with pore sizes of 1–2 mm, both thermal and plasma-assisted titanium oxide thin films and partly delamination were detected. X-ray photoelectron spectroscopy analysis revealed almost stoichiometric composition and dominance of the Ti (IV) oxidation state at a 250 °C deposition temperature. Zinc oxide coatings in porous polymer model structures partly delaminate as well, while adhesion and homogeneity is higher for printed Ti-6Al-7Nb lattice structures with a 0.5-mm mesh size. Zirconium oxide coatings on Ti-6Al-4V lattice structures with a 0.8-mm mesh size are comparable to zinc oxide coatings but are mostly crystalline. This is attributed to the relatively high, 300 °C deposition temperature. The findings demonstrate potential but also limitations of combined additive manufacturing and atomic layer deposition for medicine and energy production applications. In addition, the results confirm previous studies that metallic and polymeric substrate materials and process conditions strongly influence the coating structure and composition, and individual development of each intended application is required.