PNNL

Despite being 45 percent lighter than low carbon steel, titanium remains largely unused in the automotive industry. The cost to produce a titanium alloy strong enough for automotive use is just too high. With funding from DOE’s Vehicles Technologies Office, PNNL researchers recently discovered a new technique that improves the strength of Ti185 — the world’s strongest titanium— by 10 to 15 percent. When combined with a low-cost, high-speed forming process developed by PNNL, the stronger alloy is an excellent candidate for producing lighter vehicle parts.

As described in a paper published by Nature Communications, PNNL used electron microscopy to peer deep inside the alloy’s nanostructure and see what was happening. The team then used an atom probe tomography system to see how the atoms are arranged in 3-D. Once they understood the nanostructure, the team was able to optimize the heat-treating process to arrange the atoms into a stronger framework.

"We found that if you heat treat it first with a higher temperature before a low temperature heat treatment step, you could create a titanium alloy 10 to 15 percent stronger than any commercial titanium alloy currently on the market and that it has roughly double the strength of steel," said Arun Devaraj, material scientist at PNNL.

Steel used to produce vehicles has a tensile strength of 800-900 megapascals. The 10 to 15 percent increase achieved by PNNL puts Ti185 at nearly 1,700 megapascals, or roughly double the strength of automotive steel while being almost 50 percent lighter.

"This alloy is still more expensive than steel but with its strength-to-cost ratio, it becomes much more affordable with greater potential for lightweight automotive applications," added Vineet Joshi, metallurgist at PNNL.

The team collaborated with Ankit Srivastava, assistant professor at Texas A&M's material science and engineering department, to develop a simple mathematical model for explaining how the nanostructure can result in the exceptionally high strength. When compared with the microscopy results and processing, the model led to the discovery of this strongest titanium alloy ever made.

PNNL hopes the process could be applied to other light-weight metals, such as aluminum which is less expensive. If the nanostructure of aluminum alloys can be seen and arranged in a similar manner as the titanium alloy, stronger aluminum alloys for automobiles could be developed.

See the PNNL press release for more information.

PNNL Research Team: Arun Devaraj, Vineet V. Joshi, and Curt Lavender