High-Pressure Exposure Yields Stronger & Lighter Metal Alloys Says New Study

By Lester Mondragon | May 27, 2017 07:36 AM EDT

Scientists and metallurgists had been looking for the third atomic structure that eludes them. The arrangement of atoms in metal alloys is an indication that the real properties of metals and alloys determine its strength, brittleness, ductility, and malleability among its features. The new study led the researchers to the most sought after atomic arrangement, by high-pressure exposure.

The blending of metals also improved the properties of metal alloys compared to single elements when subjected to high-pressure exposure. An example of this is when tin mixes with copper to produce bronze or when carbon fuses with iron yielding steel. The products result is stronger and lighter metal alloys, more resistant to radiation, corrosion, and heat. The process could attribute to rare magnetic, electrical or mechanical properties.

Present atomic structures are low entropic on metal alloys. Due to the metals' disarray of atoms packing arrangement, properties could tell when an alloy is stiff or ductile, brittle or strong.

According to Cameron Tracy, first author of the study, a postdoctoral researcher at Stanford's School of Earth, Energy and Environmental Sciences and the Center for International Security and Cooperation, some of the alloys are structurally packed in metals where atoms are not in order of arrangement.

Packing structures of most high entropy metal alloys were identified in only two modes of arrangement: the body centered cubic and fast centered cubic. Until now, the third packing structure had been eluding scientists and metallurgists. Tracy and her team's study ushers the achievement of producing a high entropy metal alloy by high-pressure exposure. They published their results in the journal "Nature Communications". The new high entropy metal alloy is made up of common metals calling the atomic arrangement as hexagonal close-packed structure (HCP), reports Science Daily.

Some high entropy metals were produced in the past containing alkali and rare earth metals. Tracy claims that their resultant metal alloy is made of readily available and common metals. Their team managed to create the new hexagonal close-packed structure for engineering applications by high-pressure exposure.

The materials achieved HCP structure when subjected to high-pressure exposure beginning at 55 Giga pascals. The high pressure causes the transformation of atomic arrangement into an HCP structure that cannot be done under normal conditions. Atoms have their own magnetic pulls that hinder them to pack closely. High-pressure exposure tends to cancel magnetic properties among atoms triggering them to pack closely in hexagonal formation. The high compression force suddenly makes an HCP environment, reports Physics.Org.

The final stage of metal alloys remains after removing the pressure indicating HCP structural stability. According to Wendy Mao, co-author of the study and associate professor of Geological Science at Stanford's School of Earth, Energy, and Environmental Sciences, metals tend to return to its original state when pressure is removed, but in the new process, it is not happening. The more the pressure, the more closely packed are the structures.

Future scientists will find the results helpful to guide them in trying more alloyed metals. The main subject is the high-pressure impact that made all the difference, adds Mao.

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