Researchers at the University of Toronto Engineering have developed a metal composite that combines low weight with high strength, even at high temperatures. Its microstructure is inspired by reinforced concrete, using advanced 3D metal printing techniques to create a design that could be useful in aerospace and other high-performance industries.
“Steel rebar is widely used in the construction industry to improve the structural strength of concrete in buildings and other large structures,” adds Professor Yu Zou (MSE), senior author of a paper in Nature Communications. He explains that AM has “now enabled us to mimic this structure in the form of a metal matrix composite. This approach gives us new materials with properties we’ve never seen before.”
Rebar-Inspired Design
Aluminum is often used in aircraft for its low weight, while steel dominates ground transportation. Reducing weight while retaining strength has improved fuel efficiency, but aluminum alloys typically lose performance at high temperatures.
“Basically, the hotter they get, the softer they get, rendering them unsuitable for many applications,” says Chenwei Shao, a research fellow in Zou’s lab and lead author of the study.
To address this, the team created a composite with a mesh of titanium alloy struts, acting like rebar in concrete, surrounded by a matrix of aluminum, silicon, and magnesium. Because the team used selective laser melting (SLM) technology, they were able to produce the mesh “any size we want. The struts can be as small as 0.2 millimetres in diameter,” Shao explains. Microscopic alumina and silicon particles embedded in the matrix provide additional reinforcement, similar to the gravel in concrete.
Strength Under Pressure
Testing confirmed that the composite maintains high strength across a wide temperature range. “At room temperature, the highest yield strength we got was around 700 megapascals; a typical aluminum matrix would be more like 100 to 150 megapascals,” Shao says. “At 500 Celsius, it has a yield strength of 300 to 400 megapascals, compared to about 5 megapascals for a traditional aluminum matrix. In fact, this new metal composite performs about as well as medium-range steels, but at only about one-third the weight.”
Computer simulations led by co-author Huicong Chen identified a different deformation mechanism at high temperatures, which the team calls enhanced twinning. This “enables the material to maintain much of its strength, even when it gets very hot,” Chen says.
Zou noted that although it could take a while before industry adopts the new material, its development highlights the benefits of AM. “We wouldn’t have been able to make this material any other way. It’s true that it still costs a lot to create materials like this at scale, but there are some applications where the high performance will be worth it. And as more companies invest in advanced manufacturing technologies, we will eventually see the cost come down.”
New Metals, New Possibilities
Alongside the University of Toronto’s work, other teams are exploring ways to enhance metal performance. In October, researchers at the Massachusetts Institute of Technology (MIT) developed a new aluminum alloy. Led by S. Mohadeseh Taheri-Mousavi, the team showed that combining aluminum with small amounts of erbium, zirconium, nickel, yttrium, and ytterbium produces short-lived structures that form fine, stable particles, strengthening the metal.
Last month, U.S. Department of Energy‘s Oak Ridge National Laboratory (ORNL) was been testing DuAlumin-3D, a new aluminum alloy for high-temperature automotive components. The research indicates the alloy resists cracking better than some standard aluminum alloys used in laser powder bed fusion (LPBF), while keeping similar thermal performance, potentially enabling lighter, more efficient parts in additive manufacturing.
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Image featured shows Left to right: Postdoctoral fellow Huicong Chen, Research associate Chenwei Shao and Professor Yu Zou (MSE) demonstrate samples of their new metal matrix composite. The material is light, strong and resilient under high temperatures. Photo via Tyler Irving / University of Toronto.
