Atomic Layer Deposition for Additive Manufacturing of Metals

Tim Porcelli Field Applications Engineer

Atomic Layer Deposition for Additive Manufacturing – Metal 3D Printing

Metal 3D printing is growing at an exponential rate for applications in medical, dental, automotive, aerospace, and defense industries. Bespoke components with intricate designs and unique material properties can be made with ease for a wide variety of applications by printing. The global metal 3D printing market is projected to reach ~$6 billion by 2027 as demand for these applications continue to grow.¹ Although metal 3D printing enables many new applications, the technology still suffers from: poor feedstock powder flowability, waste metal powder byproduct oxidized during the printing process, inclusions in the bulk printed material, and hot tearing of the final product. Atomic layer deposition (ALD) on metal powder feedstock materials for 3D printing provides a variety of improvement. Powder ALD improves flowability, moisture/oxidation resistance, sintering interfaces and reduces inclusions.

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ALD IMPROVES METAL 3D PRINTING PRODUCTS

Stability

Stabilizes highly reactive metals.

Flowability

Triples the flowability of an amorphous material.

Precision

100% conformal and pin hole free.

Rheology – Moisture resistance, flowability, compaction, dispersion, cohesion
Reduced reflectivity
Reduction in oxidation
Improved sintering ability
Smaller and uniform grain boundaries
Fewer inclusions
Oxide dissolving into bulk material benefits
Expanded materials of selection for printing

ALD FOR FLOWABILITY

Variability in feedstock properties can lead to uneven layering of particles in a powder bed resulting in inconsistent bulk density, leading to lower tensile strength products and hot-tearing of material. Flowability of feedstock powder impacts the final printed product, ALD can improve the flowability of powder without chemically changing the bulk particle. In a 2019 study, five TiO₂ ALD layers on the particle surface were enough to quadruple the flowability of a partially crystalline material and to triple the flowability of an amorphous material, yet the coating process did not change the solid form of the materials and did not affect other critical characteristics related to the functionality of the materials.²

ALD FOR OXIDATION REDUCTION

Metal powders can undergo rapid oxidation during several phases of production which significantly reduces the quality of the final printed product. In powder bed fusion, specifically, bordering particles to the laser radius may be exposed to high heat without sintering which increases the native oxide thickness and hinders future sintering or reuse of powder substrate. With the ability to form dense, pinhole-free films, ALD significantly reduces oxidation of pure metals in high temperature environments. In one study, oxidation trials revealed that 20-nm-thick Al₂O₃ films deposited at a substrate temperature as low as 100°C suppress oxidative attack on pure copper and also showed excellent durability of adhesion strength.³ In a different study from Institute of Energy and Climate Research in Jülich, Germany, a ZrO₂ ALD film protected pure nickel from oxidation in an extreme fuel cell environment.⁴ Adding ALD coatings to feedstock metal powder can significantly decrease oxidation thickness which will lead to more uniform sintering and less inclusions.

In a test performed by Forge Nano, Ti64 was oxidized in a thermogravimetric analysis (TGA) environment, where oxygen was dosed through the powder as the weight of the powder was studied. As the temperature rose, the powder mass increased as the titanium metal began to oxidize to TiO₂. The uncoated titanium oxidized rapidly starting around 200°C.

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1 “3D Printing Metal Market | Reports and Data: The Increasing Use of 3D Printing in the Automotive and Aerospace Sectors” NASDAQ OMX’s News Release Distribution Channel, 21 Sept. 2020. ProQuest Central

2 “Improving Powder Characteristics by Surface Modification Using Atomic Layer Deposition” Cosima Hirschberg, Nikolaj S lvk r Jensen, Johan Boetker, Anders stergaard Madsen, Tommi O. K ri inen, Marja-Leena K ri inen, Pekka Hoppu, Steven M. George, et Al, Organic Process Research & Development 2019 23 (11), 2362-2368

3 M.L. Chang, T.C. Cheng, M.C. Lin, H.C. Lin, M.J. Chen, Improvement of oxidation resistance of copper by atomic layer deposition, Applied Surface Science, Volume 258, Issue 24, 2012, Pages 10128-10134, ISSN 0169-4332, https://doi.org/10.1016/j.apsusc.2012.06.090

4 Thomas Keuter, Georg Mauer, Frank Vondahlen, Riza Iskandar, Norbert H. Menzler, Robert Va en, Atomic-layer-controlled deposition of TEMAZ/O2–ZrO2 oxidation resistance inner surface coatings for solid oxide fuel cells, Surface and Coatings Technology,Volume 288,2016,Pages 211-220,ISSN 0257-8972, https://doi.org/10.1016/j.surfcoat.2016.01.026.