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Additive manufacturing (AM) of alloys such as stainless steels has the potential to be a disruptive technology for design of complex structures which eliminates the potentially damaging effects of mechanical failure and localized corrosion associated with interfaces between separate parts (which can now be printed as part of a single assembly). In addition, increasingly complex geometries can be manufactured with nearly as much ease as simple ones, and new mechanisms for optimization and generative design can allow manufacturers to achieve significant material and weight savings. However, challenges remain, in particular due to the potential for material variabilities both between parts made with the same nominal build parameters and even within a single build, as the consistency in properties inherent in the commercial-scale forging of alloys to be machined into components is exchanged for the considerable advantages of on-site, distributed custom parts production. Our studies and related work by other groups indicates that this is clearly true in the case of corrosion susceptibility in AM alloys. By studying the relationship between build parameters and electrochemical properties, we propose that it will be possible to tailor alloys for enhanced corrosion properties. AM processes produce materials with hierarchical microstructures containing fusion boundaries at the macroscale, irregular grains and grain boundaries at the microscale, and subgrain dislocation structures at the nanoscale. In laser powder bed fusion (LPBF) formed 316L stainless steel structures, corrosion performance has been discussed in the context of chemical heterogeneities formed in the presence of these hierarchical microstructures. However, the large variability in reported measurements underscores the need for statistically significant microstructural data, which is often difficult to access via electron microscopy alone. In this presentation, we explore multi-modal synchrotron X-ray techniques for quantifying hierarchical microstructures and their connection to the underlying chemical distribution in 316L stainless steel. Our results show that the dislocation density depends on the printing conditions with implications for the chemical distribution at the nanoscale, which in turn may play a key role in inconsistent corrosion behavior. LPDF 316L samples formed at varying speeds using pulsed and continuous laser deposition are compared via cyclic polarization in 3.5% NaCl and 0.1M HCl solutions, as well as using standard methods for characterizing sensitization. Surface corrosion layers are characterized using laboratory-based X-ray photoelectron spectroscopy to determine the impact on passivity of the aforementioned microsegregation associated with process-induced microstructures. Corrosion rates and pit densities are then discussed to build a connection between printing conditions and corrosion performance vis-à-vis microstructural and chemical information from synchrotron measurements performed at Brookhaven National Laboratory (BNL), including high energy X-ray diffraction using the X-ray Powder Diffraction (XPD) beamline at the National Synchrotron Light Source-II (NSLS-II) which provided data on minor precipitate population(s), atomic structure and dislocation microstructures critical to corrosion behavior. In addition, heterogeneities in elemental composition data is provided by 2D X-ray fluorescence (XRF) and 2D X-ray Absorption Spectroscopy (XAS) nanometer resolution-mapping obtained at the Hard X-ray Nanoprobe (HXN) beamline at the NSLS-II and correlated with process-induced hierarchal structures via use of the microscopy facilities at the Center for Functional Nanomaterials (CFN). By employing a combination of multi-modal synchrotron characterization techniques, electron microscopy, and baseline testing protocol combined with electrochemical polarization experiments, we are able to study the the role of microstructure across multiple length scales on electrochemical properties and corrosion performance. Understanding the impact of microstructure and chemical heterogeneities on the susceptibility to pitting and intergranular attack will enable microstructurally-informed process optimization and materials design for enhancing the corrosion resistance of LPBF 316L stainless steel, with implications for AM and subsequent durability of alloys in general.

In-situ characterization of electrode material under electrochemical reaction provides the unique opportunity to understand the material structure evolution under operation condition, which gives fundamental understandings of the material property and its relation to battery performance. By taking advantages of the state-of-art synchrotron X-ray techniques, it is highly accessible to investigate the chemical information and structural information with high spatial resolution and sensitivity when a suitable electrochemical cell is designed. In this work, we proposed a cell design that is capable to do 3D tomography, X-ray absorption spectra (e.g. XANES and EXAFS), and powder or single crystal diffraction under electrochemical reaction. Specifically, we will take the advantages of using Hard X-Ray Nanoprobe (HXN) with a spatial resolution of 15 nm that is recently commissioned at National Synchrotron Light Source-II to investigate the phase transition of LiFePO4 and stress-strain analysis of other electrode materials through nanodiffraction.

The Hard X-ray Nanoprobe (HXN) beamline at the NSLS-II is constructed to explore new frontiers of the x-ray microscopy, by enabling an unprecedented spatial resolution of ~10 nm in the hard x-ray regime. The beamline offers simultaneous multi-modality imaging capabilities including x-ray fluorescence, x-ray diffraction, x-ray absorption, x-ray scattering, phase-contrast imaging, spectroscopy, and ptychography. These suite of imaging tools open up new scientific opportunities to visualize complex nanostructures with unprecedented sensitivity to material composition, morphology, crystalline phases/strain, and chemical state. Use of hard x-rays allows accurate quantification of buried nanostructure with straightforward analyses. Presentation will describe the present and near-future scientific capabilities of this new imaging facility with the recent results.

With the state-of-art synchrotron-based X-ray and modern electron microscopy, the spatial resolution and measurement sensitivity have been significantly improved in analyzing materials’ nanostructure, by taking advantages of the high beam flux density or the source brightness. Associated with the ever brighter beam, it also brings the opportunity to investigate the beam effect to material structure modification, which is of significant interests in view of understanding the underlying physics, and it is also important to develop proper methodologies to use these state-of-the art probes to accurately characterize the intrinsic and extrinsic properties of materials. In our work, we performed x-ray imaging experiment on single crystalline Ag2VO2PO4 battery material sample with a 15 nm resolution using the recently commissioned x-ray imaging capability at the Hard X-ray Nanoprobe Beamline at the National Synchrotron Light Source II. Probe-induced electrochemical reaction was observed, which was revealed by the Ag reduction as well as diffusion and re-distribution of Ag. In order to better understand the probe-induced electrochemical reactions, we also performed imaging experiments with other imaging methods: white-beam microdiffraction, transmission x-ray microscopy (TXM), and transmission electron microscopy (TEM). These probes deliver different levels of radiation does and provides different pathways for probe-induced structural modification. This presentation will elaborate and quantify the probe-specific structural modifications.