Microgalvanic Corrosion Behavior of Cu-Ag Active Braze Alloys Investigated with SKPFM

Kvryan, Armen; Livingston, Kari; Efaw, Corey M.; Knori, Kyle; Jaques, Brian J.; Davis, Paul H.; Butt, Darryl P.; Hurley, Michael F.

doi:10.3390/met6040091

Cited by 18 publications

(16 citation statements)

References 36 publications

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“…Sample preparation.-Proof of concept SKFPM was performed on a commercial 316L stainless steel coupon separated and thermally re-joined with an active brazing Cu-Ag-Ti alloy (further description of the sample is provided elsewhere). 44 The effect of polishing and sam ple preparation on VPDs has been previously observed and reported. 67 To minimize effects such as metal passivation and/or adsorbed species on the variability of acquired VPD values, the sample was prepared us ing the same steps for each map acquisition.…”

Section: Methodsmentioning

confidence: 92%

“…Elemental mapping of the Cu-Ag-Ti braze region with SEM/EDS revealed a two-phase eutectic structure of copper-rich regions embedded within a silver-rich matrix, with titanium (a wetting agent) diffusing to the braze-steel interface ( Figure 4). 44 Thus, two distinct phases can be readily distinguished on the surface of the sample -a copper-rich phase (Cu-rich) and a silverrich phase (Ag-rich). Note that micro-segregation is still evident in this sample, meaning that each phase is rich in a certain element, but is still alloyed.…”

Section: Relative Work Functions Of Different Metallic Constituents-mentioning

confidence: 99%

“…(a) VPD results for copper-rich and silver-rich regions on the braze sample obtained with three different PFQNE-AL probes as seen inFigure 7and from Kvryan et al44 (b) VPD results for the same three probes acquired from the gold of the Al-Si-Au standard presented on the left ordinate axis, with resulting modified PFQNE-AL work function values presented on the right ordinate axis, as calculated with the shown equation. (c) VPDs scaled relative to the gold of the Al-Si-Au standard imaged prior to imaging of the braze sample.…”

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confidence: 99%

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Toward Improving Ambient Volta Potential Measurements with SKPFM for Corrosion Studies

Efaw

Silva

Davis

et al. 2019

J. Electrochem. Soc.

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Scanning Kelvin probe force microscopy (SKPFM) is used in corrosion studies to quantify the relative nobility of different mi crostructural features present within complex metallic systems and thereby elucidate possible corrosion initiation sites. However, Volta potential differences (VPDs) measured via SKPFM in the literature for metal alloys exhibit large variability, making inter pretation and application for corrosion studies difficult. We have developed an improved method for referencing SKPFM VPDs by quantifying the closely related work function of the probe relative to an inert gold standard whose modified work function is calculated via density functional theory (DFT). By measuring and tracking changes in the probe vs. gold VPD, this method compensates for some of the complex effects that cause changes in an individual probe's work function. Furthermore, it provides a path toward direct, quantitative comparison of SKPFM results obtained by different researchers. Application of this method to a Cu-Ag-Ti eutectic braze of a steel sample imaged with multiple SKPFM probes of differing compositions led to enhanced repeatability both within and among probe types, as well as enabled the calculation of modified work function values for each of the microstructural constituents present.

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Section: Methodsmentioning

confidence: 92%

Section: Relative Work Functions Of Different Metallic Constituents-mentioning

confidence: 99%

mentioning

confidence: 99%

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Toward Improving Ambient Volta Potential Measurements with SKPFM for Corrosion Studies

Efaw

Silva

Davis

et al. 2019

J. Electrochem. Soc.

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“…Joints formed by brazing offers as an alternative to common joining techniques, such as mechanical fastening and welding. The sample is further described elsewhere (20). The sample was polished with progressively finer silicon carbide pads from 400 to 1200 grit.…”

Section: Experimentationmentioning

confidence: 99%

Improving the Relative Calculations of Volta Potential Differences Acquired from Scanning Kelvin Probe Force Microscopy (SKPFM) from Comparing an Inert Material to First-Principle Calculations

Efaw¹,

Silva²,

Davis³

et al. 2018

ECS Trans.

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An improved relative scaling of Volta potential differences (VPD) acquired from scanning Kelvin probe force microscopy (SKPFM) was developed by quantifying the probe work function. In corrosion studies, SKPFM has been used to identify local nobility of complex metallic systems and provide theoretical corrosion initiation sites. However, large variability in measured VPD values for metallic phases has led to controversy in their interpretation. Tracking changes of the probe work function has been shown to decrease the variability seen in SKPFM results. To quantify the work function of SKPFM probes, the measured VPD of an inert gold standard was compared to the work function theoretically calculated by density functional theory (DFT) first-principles. For proof of concept, a stainless steel sample joined by a Cu-Ag-Ti brazing material was characterized by SKPFM with three different types of probes.

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“…[7][8][9] Scanning Kelvin Probe Force Microscopy (SKPFM) SKPFM imaging was conducted using a Bruker Dimension Icon AFM operating in frequency modulation (FM) PeakForce KPFM mode. [10][11][12] After polishing, each test coupon was cleaned with UHP N 2 prior to imaging to remove any loose surface particulates. A PeakForce amplitude of 75 nm and a lift height of 85 nm were used to acquire the topography and surface potential images, respectively.…”

Section: Alloys and Sample Preparationmentioning

confidence: 99%

Phase Separation in Ti-6Al-4V Alloys with Boron Additions for Biomedical Applications: Scanning Kelvin Probe Force Microscopy Investigation of Microgalvanic Couples and Corrosion Initiation

Davis

Robles

Livingston

et al. 2017

JOM

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To investigate the effect of boron additions on the corrosion behavior of Ti-6Al-4V for potential use in biomedical implants and devices, cast samples of Ti-6Al-4V were alloyed with 0.01% to 1.09% boron by weight and subjected to hot isostatic pressing. Subsequent analysis via scanning Kelvin probe force microscopy and scanning electron microscopy/energy-dispersive spectroscopy revealed the presence of both alpha (a) and beta (b) phase titanium, enriched in aluminum and vanadium, respectively. At all concentrations, boron additions affected the grain structure and were dispersed throughout both phases, but above the solubility limit, needle-like TiB structures also formed. The TiB needles and b phase exhibited similar surface potentials, whereas that of the a phase was found to be significantly lower. Nevertheless, when subjected to high applied electrochemical potentials in saline solutions, corrosion initiation was observed exclusively within the more noble b phase.

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Microgalvanic Corrosion Behavior of Cu-Ag Active Braze Alloys Investigated with SKPFM

Cited by 18 publications

References 36 publications

Toward Improving Ambient Volta Potential Measurements with SKPFM for Corrosion Studies

Toward Improving Ambient Volta Potential Measurements with SKPFM for Corrosion Studies

Improving the Relative Calculations of Volta Potential Differences Acquired from Scanning Kelvin Probe Force Microscopy (SKPFM) from Comparing an Inert Material to First-Principle Calculations

Phase Separation in Ti-6Al-4V Alloys with Boron Additions for Biomedical Applications: Scanning Kelvin Probe Force Microscopy Investigation of Microgalvanic Couples and Corrosion Initiation

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