How may research into metal fabrication lead to more durable batteries and lighter vehicles? Everything boils down to physics. Pacific Northwest National Laboratory (PNNL) researchers are exploring the impact of physical pressures on metals by examining atomic-level changes in metals undergoing shear deformation.
The forces used to modify the shape of a metal during shear deformation also rearrange its atoms, although not in the same manner for every metal or alloy. Because atomic arrangement affects metal qualities such as strength, formability, and conductivity, knowing how atoms move during shear is an important aspect of continuing attempts to custom-build next-generation metals with specified attributes from the atom up.
These visuals provide the groundwork for understanding how shear deformation produces the better properties seen in metals manufactured using Shear Assisted Processing and Extrusion (ShAPE), a PNNL breakthrough in metals production. Metals are treated utilising shear pressures during ShAPE production to manufacture high-performance metal alloys for use in cars and other purposes.
“If we understand what happens to metals on an atomic level during shear deformation, we can use that knowledge to improve countless other applications where metals experience those same forces,” said Chongmin Wang, PNNL Laboratory fellow and leader of the research team studying the forces of induced shear deformation.
Atomic puzzles
Physical forces exist everywhere. The stresses deliberately exerted during metal manufacture to form alloys are the same forces that may damage structures within batteries, causing ultimate failure. Researchers also know that shear deformation may fundamentally modify the microstructure of metals in ways that enhance the material by making it stronger, lighter, and more flexible. But how it occurs is still unknown.
“If you took a photo of a track runner at the start and conclusion of their race, you may believe they didn’t move at all,” PNNL materials scientist Arun Devaraj stated. “However, if you film the runner as they go around the track, you’ll know exactly how far they travelled.” “The same is true here: if we understand exactly what happens to metals on the atomic level during shear deformation, we could strategically apply that knowledge to design materials with specific properties.”
Gold as a standard
Researchers utilised a customised probe inside a transmission electron microscope at PNNL, one of only a few facilities in the world with this capacity, to see how shear deformation rearranges metal atoms. The researchers utilised a microscope to capture the movement of individual rows of atoms inside metals during shear deformation. They began with gold, the standard since it is the simplest to visualise on an atomic level.
When researchers saw gold being sheared, they noticed that the crystals of gold were separated into smaller grains. Natural imperfections in the arrangement of gold atoms influenced how shear deformation transported the atoms, they discovered. This is significant knowledge since flaws are frequent in metals during deformation, but they do not behave consistently across metals, which may have a direct impact on metal characteristics.
“Defects in crystal, grain size, and microstructure in a metal may alter the metal’s properties, such as strength and toughness,” said Shuang Li, PNNL postdoc and first author on three articles that shared similar findings.
The researchers next looked at copper. They studied how shear deformation produces nano twins, which are structural characteristics that make metals stronger. They discovered that shear deformation affects atoms differently within the copper and niobium phases of a metal combination by observing an alloy of copper and niobium. This is an important understanding that may help to determine how to make alloys with specified characteristics through shear deformation.
The knowledge obtained from researching how these pressures impact metals during regulated production processes may be immediately translated and applied everywhere metal is subjected to the same physical stresses. The atomic-level visualisation capabilities at PNNL, for example, is important for understanding how materials used in severe environments (e.g., nuclear reactors) or clean energy applications (e.g., hydrogen transmission lines and storage tanks) would respond to external stressors. A better understanding of the atomic physics of metal manufacture might lead to longer-lasting batteries, lighter alloys for more efficient cars, and the unique creation of next-generation metals with greater strength and conductivity.
These findings are published in three journals: Scripta Materialia (in-situ TEM observation of shear-induced microstructure evolution in Cu-Nb alloy), Acta Materialia (reversible formation of low angle grain boundary upon reciprocating shear load), and Materials Research Letters (in-situ TEM observation of deformation twin associated sub-grain boundary formation in the copper single crystal under bending).
