Close-ups of grain boundaries reveal how sulfur impurities make nickel brittle

ScienceDaily | 7/17/2018 | Staff
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The study was led by Jian Luo, a professor of nanoengineering and materials science and engineering at the UC San Diego Jacobs School of Engineering. The work is published July 17 in Nature Communications.

Since the early 1900s, engineers and scientists have recognized that sulfur impurities cause nickel and other ductile metals, such as iron and steel, to fail at low stress levels. Sulfur embrittlement of metals is of general technological importance because many engineered alloys are used in sulfur-bearing environments, such as the nickel-based high-temperature alloys used in next-generation coal-fired power plants for increasing energy efficiency.

Researchers - Embrittlement - Grain - Segregation - Sulfur

Researchers have known that this embrittlement is related to the grain boundary segregation of sulfur, but the underlying atomic mechanisms have remained elusive.

UC San Diego engineers have shed new light on these mechanisms by examining general grain boundaries in nickel polycrystals doped by sulfur. They used a combination of aberration-corrected scanning transmission electron microscopy and semi-grand-canonical ensemble atomistic simulations.

Luo - Team - Competition - Ordering - Leads

Luo's team found that competition between interfacial ordering and disordering leads to the alternating formation of amorphous-like and bilayer-like facets at general grain boundaries. They also found that bipolar interfacial structures cause brittle intergranular fractures between polar sulfur-nickel structures that are disorderly aligned in two opposite directions.

"Similar mechanisms may cause grain boundary embrittlement in other metal-nonmetal systems. Examples include oxygen, sulfur, phosphorus and hydrogen embrittlement of other metals and alloys. These are...
(Excerpt) Read more at: ScienceDaily
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