A team of researchers at the University of Toronto has discovered a new set of metal alloys that retain their strength under extreme conditions.
The materials, discovered using artificial intelligence, are well-suited to 3D metal printing and could lead to enhanced, custom-made parts for the aerospace and power generation industries, among others.
"There's enormous demand for materials that can stand up to huge swings of temperature and pressure, such as what you would find inside a jet engine, or in the steam generators inside nuclear power plants - anywhere conventional steel just can't survive," says project lead Yu Zou, an associate professor in the department of mechanical and industrial engineering in the Faculty of Applied Science & Engineering.
"We also need materials that can be printed layer by layer, enabling us to make components that can't be created by traditional manufacturing processes. For example, to make a material that is both lightweight and strong, you can vary the composition: a hard, tough alloy on the outside to something softer and lighter on the inside."
Zou, who holds the Canada Research Chair in materials and manufacturing for extreme environments, says that many of the high-performance metal alloys used today are made primarily of a single component -often nickel or cobalt - with small amounts of up to 10 other elements mixed in.
But there are many other formulations that haven't yet been explored given the vast number of possible combinations of elements.
To overcome this problem, Zou's team worked with Jason Hattrick-Simpers, a professor in the department of materials science and engineering, to create a self-driving lab capable of following up on promising leads with minimal human intervention. Their project - which combines computer modelling, machine learning and robot-assisted manufacturing - is supported by U of T's Acceleration Consortium , an institutional strategic initiative that uses AI and automation to accelerate the discovery of materials.
"One problem you often run into when trying to use AI to design materials is that most machine learning models require lots of data about material properties to learn from," says Ajay Talbot, a PhD student in Zou's lab who is lead author on a paper describing the work that was recently published in the journal npj Advanced Manufacturing. "But if you're working in part of the design space that hasn't been explored yet, that data doesn't exist, so you're kind of flying blind.
"The way we get around that challenge is to use data-lean models that essentially feel their own way along. Our active learning model strategically selects a few samples to manufacture and test, and the data from those experiments is ingested back into the model to inform where we're going to go next. It really speeds things up."
Talbot and his collaborators targeted what they call "compositionally complex alloys" that contain relatively large amounts of just three different elements: nickel, cobalt and chromium. In just a few weeks of work, their self-driving lab had zeroed in on six new alloys with promising new properties.
"One of the properties we were targeting was puncture resistance at temperatures of up to 600 C, which is what you'd find in the front section of a jet engine," says Talbot. "The industry standard in this space is nickel-based alloys such as Inconel 625. But we found one made of 12 per cent nickel, 62 per cent cobalt and 26 per cent chrome that was great for retaining hardness at extremely high temperatures. Even with just three components, our alloy outperformed Inconel 625 - an alloy of more than 10 different elements - by 4.5 per cent in our lab tests."
Another alloy is designed for the back of jet engines, where temperatures can get even hotter, up to 1,000 C.
"One of the things that happens in an environment like that is the formation of oxide scale, which essentially means that your material is just getting burnt away," says Talbot. "We found a material made of 36 per cent nickel, 14 per cent cobalt and 50 per cent chrome that was extremely good for oxidation resistance at these high temperatures: it even outperforms Inconel 625 by 85 per cent. We're eventually aiming to ramp up to even higher temperatures - up to 1,200 C."
Talbot says that the new alloys reported in the paper are just the beginning.
"This nickel-cobalt-chrome system has just three elements in it. In the grand scheme of things, it's a relatively simple system," he says. "But it's great for showing that this whole closed-loop discovery platform really works. What we want to do next is ramp up the complexity a bit more to make even crazier stuff, with maybe up to 10 or 12 different elements."
"As you add more components, you can get different strengthening mechanisms, different kinds of useful properties. There's a lot more out there just waiting to be discovered."
