Corrosion is a ubiquitous failure mode of materials. Often, the progression of localized corrosion is accompanied by the evolution of porosity in materials previously reported to be either 3D or 2D. In a new study, scientists from the Lawrence Berkeley National Laboratory, the Pennsylvania State University and elsewhere experimentally show and mechanistically explain the origin of a form of highly localized penetrating corrosion in a nickel-chromium alloy attacked by molten fluoride salt. They term this phenomenon 1D wormhole corrosion, named not only for its wormhole-like 1D morphology but also because it can function as a mass-flow pathway.
“Corrosion, a ubiquitous failure mode of materials, is traditionally measured in three dimensions or two dimensions, but those theories were not sufficient to explain the phenomenon in this case,” said Dr. Yang Yang, a researcher with the National Center for Electron Microscopy at Lawrence Berkeley National Laboratory and the Materials Research Institute at the Pennsylvania State University.
“We found that this penetrating corrosion was so localized, it only existed in one dimension — like a wormhole.”
“Corrosion is often accelerated at specific sites due to various material defects and distinct local environments, but the detection, prediction and understanding of localized corrosion is extremely challenging,” added Professor Andrew Minor, a researcher at Lawrence Berkeley National Laboratory and the University of California Berkeley.
The researchers hypothesized that wormhole formation is linked to the exceptional concentration of vacancies — the empty sites that result from removing atoms — in the material.
To prove this, they combined 4D scanning transmission electron microscopy with theoretical calculations to identify the vacancies in the material.
Together, this allowed the researchers to map vacancies in the atomic arrangement of the material at the nanometer scale.
The resulting resolution is…
Read the full article here