Super strong and lightweight metal composite material can withstand extreme heat.

Researchers at the University of Toronto have designed a new composite material that is extremely light and extremely strong, even at temperatures up to 500 degrees Celsius.

The material, described in a paper published in Nature Communications, is made of various metal alloys and nanoscale precipitates and has a structure similar to reinforced concrete, but on a microscopic scale.

These properties can make them very 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,” says Yu Zou, lead author of the study and associate professor in the Department of Materials Science and Engineering at U of T’s School of Applied Science and Engineering.

“New techniques such as additive manufacturing, also known as 3D metal printing, now allow us to mimic this structure in the form of metal matrix composites. This approach yields new materials with properties never seen before.”

Why lightweight materials are important in aerospace

While steel remains the primary structural material for trains and automobiles, aluminum’s lighter weight offers some advantages in aircraft.

Lightweighting (reducing the weight of a component while maintaining its strength) means less power is required to move the vehicle, resulting in better fuel efficiency. This is especially important in aerospace, where every gram counts.

But aluminum alloys also have drawbacks, explains Chenwei Xiao, a researcher in Zou’s lab and lead author of the new paper.

“Traditionally, aluminum parts have degraded in performance at high temperatures,” Shao says. “Basically, the higher the heat, the softer it becomes, making it unsuitable for many applications.”

How are new composite materials made?

To overcome this problem, the team aimed to construct a composite material of different metals with the same structure as reinforced concrete. A cage or mesh made of reinforcing steel is surrounded by a matrix of cement, sand, and aggregate.

“In our material, the ‘rebar’ is a mesh made of titanium alloy struts,” says Shao. “We can create this mesh to any size we want because we use a form of additive manufacturing in which metal powder is heated with a laser to heat it into a solid metal. The struts can be as small as 0.2 millimeters in diameter.”

To fill the spaces between these pillars, the team used a technique known as microcasting to create a matrix of other elements such as aluminum, silicon, and magnesium. This matrix acts like the cement that holds everything together.

Additional strength is provided by micrometer-sized particles of alumina and silicon nanoprecipitates embedded in a “cement” matrix. These particles are very similar to the gravel and aggregate found in concrete.

Testing and performance at high temperatures

The team then conducted various tests on the new material to determine its strength.

“The maximum yield strength we obtained at room temperature was about 700 megapascals, compared to around 100 to 150 megapascals for a typical aluminum matrix,” Shao says. “But it’s at high temperatures that it really shines. At 500 degrees Celsius, it has a yield strength of 300 to 400 megapascals, compared to about 5 megapascals for traditional aluminum base materials.

“In fact, this new metal composite performs almost as well as intermediate-grade steel, but weighs only about a third.”

The material’s ability to withstand degradation at such high temperatures was surprising, so the researchers built detailed computer models to understand the underlying mechanisms.

“What we found is that at high temperatures, this composite material deforms by a different mechanism than most metals,” says study co-author Huikong Chen, who led the computer simulations. “We called this new mechanism ‘reinforcement twinning,’ and it allows the material to retain much of its strength even at very high temperatures.”

Looking to industrial applications

Zou said that while it may be some time before new materials start being introduced in industry, the discovery highlights the benefits of newly emerging technologies such as additive manufacturing.

“We couldn’t have made this material any other way,” he says. “While it’s true that creating materials like this at scale still costs a lot of money, there are some applications where the high performance is worth it. And as more companies invest in advanced manufacturing techniques, we’ll eventually see costs come down.”

“We think this is a great step forward towards stronger, lighter and more efficient vehicles.”