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Novel Ceramic/Metallic Materials February 2015 Viewpoints

Technology Analyst: Alastair Cunningham

High-Entropy Alloy Yields World-Record Strength-to-Weight Ratio

Why is this topic significant?

High-entropy alloys represent an emerging class of material that is causing a considerable amount of excitement within the materials community. These materials—which display properties that outperform those of all other metals—could prove to be of high interest across a number of industrial sectors.

Description

In December 2014, researchers from North Carolina State University and Qatar University released the results of their research into a novel "high-entropy" alloy that they claim has a higher strength-to-weight ratio than any other metallic material has. The December 2014/January 2015 Viewpoints discusses previous developments in the field of high-entropy alloys—materials that contain at least five component elements in roughly equal amounts. The lack of one dominant constituent element yields a range of impressive properties, such as high strengths and low densities, and these materials could play a particularly important role in applications at cryogenic temperatures. The team of researchers combined lithium, magnesium, titanium, aluminum, and scandium to form their high-entropy alloy. The strength-to-weight ratio of this material approaches that of some ceramics but does not suffer from the same brittleness problems. However, the extremely high cost of scandium—which constitutes 20% of the alloy—could pose significant barriers to the commercialization of this material. The scientists' next steps will involve further research that determines whether it is possible either to replace scandium with a cheaper component or to eliminate it entirely from the final alloy.

Implications

Fundamental materials research is crucial to progress within almost all industrial sectors and can drive innovation in a number of existing—or even result in the creation of new—commercial applications. The development of this high-entropy alloy with record-breaking properties will therefore be of high interest to many groups that require high-strength and low-density materials. For example, such properties make materials such as these of great interest for prosthetics applications—where high strength, low density, and biocompatibility represent the key factors on which developers judge the merits of novel materials. Alternatively, such high-entropy alloys could be of great interest to developers within the automotive industry—with lightweighting and safety being two of the principal concerns. The high price of scandium is likely to make the North Carolina State University alloy prohibitively expensive for some mass-market applications. However, other applications in the defense or aerospace industries—where material performance rather than cost is of greater importance—could benefit from this research in the shorter term.

Impacts/Disruptions

Regulations governing the fuel efficiency of vehicles and carbon dioxide emissions are driving moves to commercialize high-strength, low-density materials in the automotive industry. Despite their impressive properties, high-entropy alloys are likely to face stiff competition from more established alternatives such as metal-matrix composites, ceramic-matrix composites, and polymer-matrix composites. Much work remains before high-entropy alloys see widespread use in commercial applications, and the materials currently remain a highly uncertain but potentially high-impact area of research.

Scale of Impact

  • Low
  • Medium
  • High
The scale of impact for this topic is: Medium to High

Time of Impact

  • Now
  • 5 Years
  • 10 Years
  • 15 Years
The time of impact for this topic is: 5 Years to 10 Years

Opportunitites in the following industry areas:

Energy, manufacturing, automotive, health

Relevant to the following Explorer Technology Areas:

Bulk-Metallic-Glass Project Receives Significant Funding

Why is this topic significant?

Bulk metallic glasses—already in use in a number of applications—could be on the verge of making a major commercial breakthrough. The identification of novel alloys represents the first step in this commercialization process.

Description

In November 2014, the US National Science Foundation awarded Yale University engineers a $1.2 million grant to fund a three-year project researching the properties of bulk metallic glasses. Bulk metallic glasses—or amorphous metals—are alloys that do not possess an ordered crystalline structure. Rather, the atoms within the alloy adopt an amorphous (or random) structure—much like in standard glass. The materials form through rapid cooling processes in order to inhibit the formation of crystalline regions and lock the disorder of the molten state in place. Fewer structural deficiencies than those of standard crystalline metals yield several advantages—such as reduced shrinkage rates, higher strengths, higher hardnesses, increased resistance to wear and corrosion, and enhanced processability. The Yale project will exploit computational and experimental techniques to characterize millions of potential bulk metallic glasses—representing a significant increase over the 120 000 candidates already characterized by more traditional methods. To date, the most successful bulk metallic glass identified by the researchers is platinum based and therefore extremely expensive. The discovery of a material in which the principal element is copper or aluminum is the chief goal of the project and would aid in bringing amorphous metals into more widespread commercial use.

Implications

This project—through the identification of promising alloys—is likely to accelerate the widespread commercialization of bulk metallic glasses. The discovery of novel combinations of metals that possess the advantageous properties of bulk metallic glasses and that are possible to manufacture economically at large volumes could help to grow the market for these materials as well as creating competition for the products that are already available. For example, the company Liquidmetal Technologies—the "leading commercial OEM supplier of bulk amorphous alloy parts"—offers amorphous alloys that display twice the strength of titanium while maintaining the ability to "mold intricate and complex parts in one step."

Impacts/Disruptions

A key barrier to the further commercialization of bulk metallic glasses is the extra cost that their use can incur. These materials are particularly sensitive to oxidation in their molten state and, as a result, must undergo quick processing steps under high vacuum conditions. However, for parts that require high strength or that have complex shapes with low tolerances, the selection of an amorphous metal can prove to be an economical—or indeed, the only—choice. Bulk metallic glasses already find use in the consumer-electronics industry. Components such as device casings or hinges and clamps that have to maintain structural fidelity after thousands of cycles benefit from the unique properties of amorphous metals. Other established applications for bulk metallic glasses include wing-control surfaces for missiles, surgical tools, equipment in the oil-and-gas industry, and consumer products such as high-end sports equipment, high-strength spectacle frames, and high-durability kitchen knives.

Scale of Impact

  • Low
  • Medium
  • High
The scale of impact for this topic is: High

Time of Impact

  • Now
  • 5 Years
  • 10 Years
  • 15 Years
The time of impact for this topic is: 5 Years

Opportunitites in the following industry areas:

Health, aerospace, defense, energy, sporting goods, automotive, consumer products

Relevant to the following Explorer Technology Areas: