Oxygen robs iron alloys of strength at high temperatures

Researchers at the University of Connecticut have found that reducing oxygen in some nanocrystalline materials may improve their strength and durability at elevated temperatures. This is a promising enhancement, reported in a paper in the Journal of Alloys and Compounds, that could lead to better biosensors, faster jet engines and greater capacity semiconductors.

"Stabilizing nanocrystals at elevated temperatures is a common challenge," says Peiman Shahbeigi-Roodposhti, a postdoctoral research scholar with UConn's Institute of Materials Science and the paper's lead author. "In certain alloys, we found that high levels of oxygen can lead to a significant reduction in their efficiency."

Using a special milling process in an enclosed glove box filled with argon gas, UConn scientists, working in collaboration with researchers from North Carolina State University, were able to synthesize nano-sized crystals of iron chromium and iron chromium hafnium with oxygen levels as low as 0.01%. These nearly oxygen-free alloy powders appeared to be much more stable at elevated temperatures and under high levels of stress than their commercial counterparts with higher oxygen contents.

"In this study, for the first time, optimum oxygen-free nanomaterials were developed," explains Sina Shahbazmohamadi, an assistant professor of biomedical engineering at UConn and a co-author on the paper. "Various characterization techniques, including advanced aberration corrected transmission electron microscopy, revealed a significant improvement in grain size stability at elevated temperatures."

Grain size stability is important for scientists seeking to develop the next generation of advanced materials. Like fine links in an intricately woven mesh, grains are the small solids from which metals are made. Studies have shown that smaller grains are better when it comes to making stronger and tougher metals that are less prone to cracking, better at conducting electricity, and more durable at high temperatures and under extreme stress.

Recent advances in technology have allowed materials scientists to develop grains at the scale of just 10nm. Such nanocrystals can only be viewed under extremely powerful microscopes.

But the process isn't perfect. When some nanograins are created in bulk for applications such as semiconductors, the stability of their size can fluctuate under higher temperatures and stress. It was while investigating this instability that Shahbeigi-Roodposhti and the UConn research team learned the role oxygen played in weakening the nanocrystals' stability at high temperatures.

"This is only a first step, but this line of investigation could ultimately lead to developing faster jet engines, more capacity in semiconductors and more sensitivity in biosensors," Shahbeigi-Roodposhti says.

Moving forward, the UConn researchers intend to test their theory on other alloys to see whether the presence or absence of oxygen impacts their performance at elevated temperatures.

This story is adapted from material from the University of Connecticut, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.