Turning up the heat on titanium alloy leads to increase in strength
Looking deep inside titanium alloy has allowed researchers at the Pacific Northwest National Laboratory (PNNL) to manipulate the alignment of atoms and develop the strongest titanium alloy ever made. They believe the new material could be used in the production of lighter and cheaper vehicle components, and lead to the development of other high strength alloys.
Titanium is almost half as light as steel used for the manufacture of vehicles and, when mixed with other metals, gains superior strength properties. Current methods of mixing titanium with other metals have been in development for 50 years, but creating reliable, well-mixed and low defect alloys such as the common Ti-185 is an expensive, energy-intensive process.
Six years ago, PNNL researchers developed a Ti-185 mix that is very high strength and defect-free. The process has since been in use by co-developer Advanced Materials (ADMA), a commercial partner which sells the advanced materials to aerospace and other industries. But the team wanted to make the alloy even stronger.
"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 10-15 percent stronger than any commercial titanium alloy currently on the market and that it has roughly double the strength of steel," said Arun Devaraj a material scientist at PNNL.
An electron microscope was used to peek inside the alloy at the hundreds of nanometers scale, followed by a closer look at the arrangement of individual atoms with the help of an atom probe tomography system. The researchers found that micron-sized and nano-sized precipitate regions were created by the optimized heat process (known as the alpha phase, in a matrix called the beta phase), each having high concentrations of certain elements.
"The aluminum and titanium atoms liked to be inside the nano-sized alpha phase precipitates, whereas vanadium and iron preferred to move to the beta matrix phase," said Devaraj. Treating these regions to temperatures of 1,450° F (788° C) is reported to have resulted in a unique hierarchical nano structure.
Strength measurements indicate that the new alloy, called hierarchical nanostructured Ti-185 (HNS Ti-185), has a tensile strength of nearly 1,700 megapascals – about twice that of steel used in automotive manufacture. The manufacture process of the new alloy is reported to require about half the time of conventional methods and utilizes relatively cheap titanium hydride powder.
"Now that we understand what's happening and why this alloy has such high strength, researchers believe they may be able to modify other alloys by intentionally creating microstructures that look like the ones in Ti185," said Devaraj.
An open access paper has been published in Nature Communications. The video below provides an overview of the research.