Ashby plot of strength vs. density
Ashby plot of strength vs. density for engineering materials. (Yield strength for metals and polymers, tear strength for elastomers, compressive strength for ceramics, and tensile strength for composites.) Reproduced with permission from Elsevier 2010

Researchers from the Qatar University and North Carolina State University have developed a new “high-entropy” metallic alloy that has a much higher strength-to-weight ratio than any other present metallic material known to man.

High-entropy alloys are materials that consist of 5 or more metals in roughly equal quantities. These alloys are at present the focus of serious consideration in materials science and engineering because they can have fascinating properties.

The NC State research team mixed magnesium, lithium, aluminum, titanium and scandium to make a nano-crystalline high-entropy alloy that has lower density, but it is very strong.

“The density is similar to aluminum, however it’s stronger than titanium alloys,” said Dr. Carl Koch, Kobe Steel Distinguished Professor of Materials Science and Engineering at NC State and lead author of a paper on the work. “It has a mix of high strength and low density that’s, so far as we can tell, unmatched by any other metallic material. The strength-to-weight ratio is akin to some ceramics, however we think it is tougher – and much less brittle – than ceramics.”

There are a variety of uses for light weight and robust materials, such as in prosthetics, aircraft or in automobiles.

“We still have a lot of analysis to do to completely characterize this material and discover the best processing strategies for it,” Koch told us.

Info about the high entropy alloy
(a) Bright field TEM image and diffraction pattern, (b) dark field image, and (c) grain size distribution of as-milled uncontaminated material.

At this point, the first downside with the alloy is that it’s manufactured from 20% scandium, which is very costly.

“One thing we will be looking at is whether or not scandium might be replaceable or eliminated from the alloy,” Koch said.

For more info: See the paper “A Novel Low Density, High Hardness, High-Entropy Alloy with Close-packed Single-phase Nanocrystalline Structures,” which is published on-line in the open-access journal Materials Research Letters. DOI: 10.1080/21663831.2014.985855



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