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Dissimilar metal welds (DMWs) are commonly used when a high strength steel is overlaid with a corrosion resistant alloy (CRA) for petrochemical applications. There have been reported failures of these DMWs during subsea service while under cathodic protection (CP). These failures are caused by local hydrogen embrittlement of susceptible microstructures that form at the weld fusion boundary. Hydrogen-assisted cracking (HAC) occurs as a result of the local embrittlement and is influenced by base/filler metal combinations, and welding and post-weld heat treatment (PWHT) procedures. A delayed hydrogen cracking test was used to simulate tensile load and hydrogen charging on 8630-FM 625 weld. The failure of this sample was recorded using a high-speed camera to capture the crack initiation and propagation during failure. Fractography was performed using a scanning electron microscope (SEM) along with energy dispersive spectroscopy (EDS). The fracture surfaces, EDS measurement and video timestamps revealed brittle fracture nucleation in the planar growth and CGHAZ regions of the weld. The cracking continued to propagate through the same regions of the weld leading to final ductile failure (microvoid coalescence) in the cellular dendritic region of the weld.
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Fracture behavior of metallic sodium and implications for battery applications
Sodium metal has emerged as a candidate anode material in rechargeable batteries owing to its high theoretical capacity, low standard reduction potential, and abundance in the earth's crust. Prior to practical deployment, it is critical to thoroughly assess sodium's mechanical properties, as to fully understand and thus help mitigate potential failure mechanisms. Herein, we examine the fracture behavior of sodium metal through tensile tests in an inert environment. We find that sodium is nearly insensitive to flaws (crack-like features), i.e. , its effective strength is virtually unaffected by the presence of flaws. Instead, under tension, sodium exhibits extreme necking that leads to eventual failure. We also characterize the microstructural features associated with fracture of sodium through scanning electron microscopy studies, which demonstrate several features indicative of highly ductile fracture, including wavy slip and microvoid formation. Finally, we discuss the implications of these experimental observations in the context of battery applications.
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- Award ID(s):
- 1944674
- PAR ID:
- 10409352
- Date Published:
- Journal Name:
- Materials Horizons
- Volume:
- 9
- Issue:
- 12
- ISSN:
- 2051-6347
- Page Range / eLocation ID:
- 3102 to 3109
- 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/10.1039/D2MH01021F
