Electrochemical atomic layer etching (e-ALE) is a unique approach for etching metals one atomic layer at a time. If practiced under optimal conditions, e-ALE ensures minimal evolution of surface roughness due to the atomic layer-by-layer etching characteristics. During e-ALE of copper (Cu), the crucial first step is the formation of a cuprous sulfide (Cu2S) monolayer via the surface-limited sulfidization reaction. In this paper, we investigate the surface coverage of this sulfide layer as a function of the sulfidization potential, and show that the equilibrium coverage attained can be modeled using the Frumkin adsorption isotherm. At a potential of –0.74 V vs SHE, sulfidization provides near-complete monolayer coverage of Cu by Cu2S, which then facilitates e-ALE in a layer-by-layer etching mode thereby maintaining a smooth post-etch surface. Operation at potentials negative with respect to –0.74 V provides sub-monolayer coverage, which manifests in roughness amplification during etching. This work provides a thermodynamics-guided foundation for the selection of operating conditions during Cu e-ALE.
Iodine-Based Sensitization of Copper Alloys to Enable Self-Terminating Etching for Support Removal and Surface Improvements of Additively Manufactured Components
Advances in selective laser melting (SLM) of metals in the past two decades have made metals additive manufacturing more accessible for industrial adoption. Despite printing process improvements, post- processing of SLM components has not improved much, resulting in considerable costs, delay, and design limitations. Building upon recent advances in sensitization-based self-terminating etching processes, this work details a new set iodine-based sensitization and etching chemistries that simplify the post-processing of copper (Cu) alloy components fabricated using SLM. This work demonstrates that iodine can be used to ‘‘sensitize’’ the surface of copper alloy components to form soluble copper iodide salt that can be then dissolved in common solvents, such as acetonitrile. This process removes a predefined amount of material from all interior and exterior surfaces in a self-terminating manner, enabling facile removal of internal and external supports, removal of any trapped powder, and the smoothing of interior and exterior surfaces. We demonstrate this process on GRCop (Cu-chromium-niobium) alloys due to their widespread use by the rocket propulsion industry along with a demonstration in copper (110) for applications in heat exchangers and electromagnetic transmitters/receivers. Our results provide the first systematic study on the effect of iodi- zation temperature and duration on the thickness of the iodide region in GRCop-84 components. Additionally, the surface roughness before and after each iodization–dissolution was also quantified for GRCop-84 and showed 70% reduction in Ra roughness from a high of 10 lm as-printed to a low of 3 lm after four iodization-dissolution cycles.
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- Award ID(s):
- 1944516
- NSF-PAR ID:
- 10403614
- Date Published:
- Journal Name:
- 3D Printing and Additive Manufacturing
- ISSN:
- 2329-7662
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1089/3dp.2021.0242
