Researchers develop unique quantum mechanical method for determining ductility of metals

A team of scientists from Ames National Laboratory and Texas A&M University has developed a new method for predicting the ductility of metals. This quantum-mechanics-based approach fulfills the need for an inexpensive, efficient, and high-throughput ductility prediction method.

The results of the study were published in Materials Letters under the title "A ductility metric for refractory-based multi-principal-element alloys".

The team demonstrated the effectiveness of this approach on refractory multi-principal-element alloys. These materials are of interest for applications at high temperatures, but they often lack the necessary ductility for applications in aerospace, fusion reactors and land-based turbines.

Ductility is the ability of a material to withstand physical strain without cracking or fracturing. According to Prashant Singh, a scientist at Ames Laboratory and head of the theoretical design effort, there is no reliable method for predicting the ductility of metals. In addition, trial-and-error experiments are expensive and time-consuming, especially under extreme conditions.

The typical approach to atomic modeling is to use symmetric rigid spheres. However, Singh explains that in real materials, atoms are of different sizes and shapes; when mixing elements with different-sized atoms, the atoms constantly adjust to fit into a fixed space. This behavior causes local atomic distortions (distortions).

The new analytical method incorporates local atomic distortions to determine whether a material is brittle or ductile. It also extends the capabilities of current methods. "For small compositional changes, they (current methods) are not efficient in distinguishing between ductile and brittle systems. But the new method can capture such non-trivial details because now we have added quantum mechanical features to the method, which were missing before." Singh explains.

Another advantage of this new high-throughput testing method is its efficiency. singh says that it can test thousands of materials quickly. This speed and capability makes it possible to predict which combinations of materials are worth experimenting with - which minimizes the time and resources needed to discover these materials through experimental methods.

To determine how well their ductility tests worked, Ames National Laboratory scientist Gaoyuan Ouyang led the team's experimental efforts. They conducted validation tests on a set of predicted refractory multi-primary element alloys (RMPEAs): materials that have the potential to be used in high-temperature environments, such as aerospace propulsion systems, nuclear reactors, turbines, and other energy applications.

The proposed LLD metric is used to characterize the ductility of bcc refractory metals.

The team found that higher (increased) charge activity is responsible for the increased ductility of body-centered cubic metals. The yellow region represents higher electronic charge in the interstitial space (the region between atoms), which corresponds to an increase in charge activity, leading to higher ductility. The light blue regions are the less charge-active interstices. In this picture, each atom is represented by a different color, such as tantalum (Ta), molybdenum (Mo) and tungsten (W) as described above. Blue, pink and red contours show the charge distribution around each site.

Through validation tests, the team found that the predicted ductile metals deformed significantly at high stresses, while the brittle metals cracked under similar loads, confirming the robustness of the new quantum mechanical method.

Reference links:

[1] https://www.eurekalert.org/news-releases/998473

[2] https://phys.org/news/2023-08-unique-quantum-mechanical-approach-metal.html