The work, by Dongchan Jang, senior postdoctoral scholar, and Julia R. Greer, assistant professor of materials science and mechanics at Caltech, could eventually lead to the development of innovative, superstrong, yet light and damage-tolerant materials. These new materials could be used as components in structural applications, such as in lightweight aerospace vehicles that last longer under extreme environmental conditions and in naval vessels that are resistant to corrosion and wear.
A paper about the work appears in the February 7 advance online edition of the journal Nature Materials.
"Historically," says Greer, "structural materials have always had to rely on their processing conditions, and thereby have been 'slaves' to their properties." For example, ceramics are very strong, which makes them great for structural applications. At the same time, these materials are very heavy, which is problematic for many applications, and they are extremely brittle, which is less than ideal for supporting heavy loads. In fact, says Greer, "they fail catastrophically under mechanical loads." Metals and alloys, on the other hand, are ductile, and therefore unlikely to shatter, but lack the strength of ceramics.
Materials scientists have developed an intriguing class of materials called glassy metallic alloys, which are amorphous and lack the crystalline structure of traditional metals. The materials, also known as metallic glasses, are composed of random arrangements of metallic elements like zirconium, titanium, copper, and nickel. They are lightweight—a "huge advantage" for their incorporation into new types of devices, Greer says—and yet are comparable in strength to ceramics. Unfortunately, their random structure makes metallic glasses quite brittle. "They also fail catastrophically under tensile loads," she says.
But now, Greer and Jang, the first author on the Nature Materials paper, have developed a strategy to overcome these obstacles—by making metallic glasses that are almost vanishingly small.
The scientists devised a process to make zirconium-rich metallic glass pillars that are just 100 nanometers in diameter—roughly 400 times narrower than the width of a human hair. At this size, Greer says, "the metallic glasses become not only even stronger, but also ductile, which means they can be deformed to a certain elongation without breaking. Strength plus ductility," she says, represents "a very lucrative combination for structural applications."
As yet, there are no immediate applications for the new materials, although it may be possible to combine the nanopillars into arrays, which could then form the building blocks of larger hierarchical structures with the strength and ductility of the smaller objects.
The work, however, "convincingly shows that 'size' can be successfully used as a design parameter," Greer says. "We are entering a new era in materials science, where structural materials can be created not only by utilizing monolith structures, like ceramics and metals, but also by introducing 'architectural' features into them."
For example, Greer is working towards fabricating a "brick-and-mortar" architecture using tiny plates of a metallic glass and ultrafine-grained ductile metal with nanoscale dimensions that could then be used to fabricate new engineering composites with amplified strength and ductility.
To use this architecture-driven approach to create structural materials with enhanced properties—that are, for example, superstrong, yet light and ductile—researchers must understand how each constituent part deforms during use and under stress.
"Our findings," she says, "provide a powerful foundation for utilizing nanoscale components, which are capable of sustaining very high loads without exhibiting catastrophic failure, in bulk-scale structural applications specifically by incorporating architectural and microstructural control."
Adds Greer: "The particularly cool aspect of the experiment is that it is nearly impossible to do! Dongchan, my amazing postdoc, was able to make individual 100-nm-diameter tensile metallic glass nanopillar samples, which no one had ever done before, and then used our custom-built in situ mechanical deformation instrument, SEMentor, to perform the experiments. He fabricated the samples, tested them, and analyzed the data. Together we were able to interpret the results and to formulate the phenomenological theory, but the credit goes all to him."
The work in the Nature Materials paper, "Transition from a strong-yet-brittle to a stronger-and-ductile state by size reduction of metallic glasses," was funded by the National Science Foundation and the Office of Naval Research, and utilized the fabrication and characterization facilities of the Kavli Nanoscience Institute at Caltech.
A materials scientist’s dream come true
21.08.2018 | Friedrich-Alexander-Universität Erlangen-Nürnberg
Novel sensors could enable smarter textiles
17.08.2018 | University of Delaware
There are currently great hopes for solid-state batteries. They contain no liquid parts that could leak or catch fire. For this reason, they do not require cooling and are considered to be much safer, more reliable, and longer lasting than traditional lithium-ion batteries. Jülich scientists have now introduced a new concept that allows currents up to ten times greater during charging and discharging than previously described in the literature. The improvement was achieved by a “clever” choice of materials with a focus on consistently good compatibility. All components were made from phosphate compounds, which are well matched both chemically and mechanically.
The low current is considered one of the biggest hurdles in the development of solid-state batteries. It is the reason why the batteries take a relatively long...
New design tool automatically creates nanostructure 3D-print templates for user-given colors
Scientists present work at prestigious SIGGRAPH conference
Most of the objects we see are colored by pigments, but using pigments has disadvantages: such colors can fade, industrial pigments are often toxic, and...
Scientists at the University of California, Los Angeles present new research on a curious cosmic phenomenon known as "whistlers" -- very low frequency packets...
Scientists develop first tool to use machine learning methods to compute flow around interactively designable 3D objects. Tool will be presented at this year’s prestigious SIGGRAPH conference.
When engineers or designers want to test the aerodynamic properties of the newly designed shape of a car, airplane, or other object, they would normally model...
Researchers from TU Graz and their industry partners have unveiled a world first: the prototype of a robot-controlled, high-speed combined charging system (CCS) for electric vehicles that enables series charging of cars in various parking positions.
Global demand for electric vehicles is forecast to rise sharply: by 2025, the number of new vehicle registrations is expected to reach 25 million per year....
17.08.2018 | Event News
08.08.2018 | Event News
27.07.2018 | Event News
21.08.2018 | Ecology, The Environment and Conservation
21.08.2018 | Life Sciences
21.08.2018 | Power and Electrical Engineering