Nav: Home

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

July 17, 2018

Engineers at the University of California San Diego have shed new light on a scientific mystery regarding the atomic-level mechanism of the sulfur embrittlement of nickel, a classic problem that has puzzled the scientific community for nearly a century. The discovery also enriches fundamental understanding of general grain boundaries that often control the mechanical and physical properties of polycrystalline materials.

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 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'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 of broad technological importance," said Luo.

This work further advances previous research by Luo's group on the bismuth embrittlement of nickel, which was done in collaboration with Lehigh University and published in two subsequent reports in Science in 2011 and 2017. Researchers discovered that highly-ordered interfacial structures form at general grain boundaries in bismuth-doped nickel. In the new Nature Communications study, Luo's group found that disordered bipolar interfacial structures form in sulfur-doped nickel.

"Bismuth and sulfur are two well-known embrittling impurities for nickel. Interestingly, we found that these represent two extreme cases of interfacial structures--ordered versus disordered, respectively. Thus, they may be considered as two classic examples of grain boundary embrittlement with different underlying atomistic structures," Luo said.

Aside from embrittlement mechanisms, researchers say this study sheds new light on the mysterious abnormal grain growth phenomena in sulfur-doped nickel, and enriches fundamental understanding of disordered interfaces. This study also challenges a traditional view by showing that the orientation of the grain boundary facet, instead of the misorientation, dictates the interfacial structure.

"This work broadens our fundamental knowledge of materials interfaces beyond the well-characterized ordered interfaces and special symmetric boundaries in artificial bicrystals that have been the focus of most prior studies. Now, we have new insight into the disordered interfaces and general grain boundaries in real-world polycrystals, which often limit the performance of most engineered materials," said Luo.
-end-
Luo is also affiliated with the Sustainable Power and Energy Center at UC San Diego, where he is working on materials related issues for both energy storage and energy efficiency.

Paper title: "Role of disordered bipolar complexions on the sulfur embrittlement of nickel general grain boundaries." Co-authors include joint co-first authors Tao Hu and Shengfeng Yang, Naixie Zhou and Yuanyao Zhang.

This work was supported by a Vannevar Bush Faculty Fellowship (N00014-16-1-2569).

University of California - San Diego

Related Sulfur Articles:

Scientists develop high-performance lithium-sulfur batteries
Recently, research groups led by Prof. LIU Jian and Prof.
Reducing sulfur dioxide emissions alone cannot substantially decrease air pollution
Due to the reduced emissions of SO2, and considering the high level of NH3 emissions in China, nitrogen dioxide emissions control is more effective in reducing the surface PM2.5 concentration in China.
Sulfur 'spices' alien atmospheres
They say variety is the spice of life, and now new discoveries from Johns Hopkins researchers suggest that a certain elemental 'variety' -- sulfur -- is indeed a 'spice' that can perhaps point to signs of life.
All-solid-state lithium-sulfur batteries with high capacity and long life
Toyohashi University of Technology researchers have made an active sulfur material and carbon nanofiber (CNF) composite using a low-cost and straightforward liquid phase process.
How plants in the cabbage family look inward when sulfur is scarce
Studying genetically modified model plants from the cabbage family, researchers at Kyushu University found that disrupting the production of two enzymes in thale cress plants growing in sulfur-deficient environments further stunts growth by reducing their ability to breakdown sulfur-containing glucosinolates.
Stabilizing sulfur cathode by single Li-ion channel polymer binder
Lithium-sulfur batteries have great potential for high-performance energy storage devices, yet the severe diffusion of soluble polysulfide in electrolyte greatly limits their practical applications.
New findings on the largest natural sulfur source in the atmosphere
An international research team was able to experimentally show in the laboratory a completely new reaction path for the largest natural sulfur source in the atmosphere.
Using high energy density material in electrode design enhances lithium sulfur batteries
To develop higher capacity batteries, researchers have looked to lithium sulfur batteries because of sulfur's high theoretical capacity and energy density.
Earth, wind, flora sway Trinidad sulfur levels
UC geologists get a glimpse into the power of wind, rain, coastal proximity and climate on coastal environments.
New study tracks sulfur-based metabolism in the open ocean
Oceanographers found that marine microbes process sulfonate, a plentiful marine nutrient, in a way that is similar to soils.
More Sulfur News and Sulfur Current Events

Trending Science News

Current Coronavirus (COVID-19) News

Top Science Podcasts

We have hand picked the top science podcasts of 2020.
Now Playing: TED Radio Hour

Clint Smith
The killing of George Floyd by a police officer has sparked massive protests nationwide. This hour, writer and scholar Clint Smith reflects on this moment, through conversation, letters, and poetry.
Now Playing: Science for the People

#562 Superbug to Bedside
By now we're all good and scared about antibiotic resistance, one of the many things coming to get us all. But there's good news, sort of. News antibiotics are coming out! How do they get tested? What does that kind of a trial look like and how does it happen? Host Bethany Brookeshire talks with Matt McCarthy, author of "Superbugs: The Race to Stop an Epidemic", about the ins and outs of testing a new antibiotic in the hospital.
Now Playing: Radiolab

Graham
If former Minneapolis police officer Derek Chauvin's case for the death of George Floyd goes to trial, there will be this one, controversial legal principle looming over the proceedings: The reasonable officer. In this episode, we explore the origin of the reasonable officer standard, with the case that sent two Charlotte lawyers on a quest for true objectivity, and changed the face of policing in the US. This episode was produced by Matt Kielty with help from Kelly Prime and Annie McEwen. Support Radiolab today at Radiolab.org/donate.