researchers at the university of connecticut (uconn) have discovered that a reduction in oxygen in some nanocrystalline materials could enhance strength and durability at high temperatures, which could lead to improved biosensors, jet engines, and higher-capacity semiconductors, according to an article on the uconn website.

postdoctoral researcher peiman shahbeigi-roodposhti (standing) and sina shahbazmohmadi,
assistant professor in biomaterials engineering, discuss grain microstructures characterized
by an advanced electron microscope. (university of connecticut)

the researchers used a special milling process in an enclosed box with argon gas to create nano-sized crystals of iron-chromium and iron-chromium-hafnium with oxygen levels that were as low as 0.01 percent. the powders appeared to be more stable than commercial materials at higher temperatures and higher levels of stress.

“grain size stability is important for scientists seeking to develop the next generation of advanced materials,” the article explained. “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 conductors of electricity, and more durable at high temperatures and under extreme stress.”

the process for creating nanocrystals has been inconsistent with nanograins created in bulk for semiconductors fluctuating in performance when placed in high temperatures or put under stress.

the researchers hope to continue testing on other alloys and see if oxygen levels affect their performances.

the uconn research was recently published in the journal of alloys and compounds. the abstract stated:

“low oxygen content powders of high purity elemental fe, cr and hf were produced in a glove box by mechanically filing the solid materials. fe10cr and fe14cr4hf nanocrystalline alloy powders were processed using these elemental powders in conjunction with spex ball milling. the grain-size stability of the nanocrystalline alloy powders was investigated for selected annealing temperatures.

“high temperature stabilization can be achieved by zener pinning (kinetic mechanism) or segregation of hf to grain boundaries (thermodynamic mechanism). solute drag mechanisms can be effective at lower annealing temperatures. recent regular solution models developed by the authors predict that hf would facilitate thermodynamic grain-size stabilization in fe14cr4hf alloys at high temperatures.

“however, hf-base reactions such as intermetallic phase or oxide formation can favor kinetic stabilization and this can dominate over a contribution from thermodynamic stabilization. in contrast, grain-size stabilization in fe10cr alloy would be a result of solute drag by the cr solutes at lower temperatures.

“the results from previous investigations on fe10cr and fe14cr4hf nanocrystalline alloys were (unknowingly at the time) influenced by the fact that the commercially available high purity elemental powders used for spex ball mill processing contained significant amounts of oxygen impurity.

“the results obtained in this investigation using identical processing methods with low oxygen content powders for synthesizing the alloys provide further insight into their stabilization mechanisms.”