Researchers at IMDEA Materials Institute have developed a new hybrid methodology that combines quantum mechanics and thermodynamic calculations to predict the phase diagram of nickel-cobalt alloys.

Published in Acta Materialia, this breakthrough overcomes the limitations of traditional methods, particularly at low temperatures, without the need for experimental data.

Nickel-cobalt (Ni-Co) alloys are essential in high-tech sectors such as energy generation and the aerospace industry due to their exceptional resistance to high temperatures and corrosion.

They are also key components of emerging High Entropy Alloys (HEAs), promising materials known for their superior mechanical properties.

However, the design of new and improved alloys has been limited by the lack of accurate knowledge of their phase diagram, the map that determines the internal structure of the material according to its composition and temperature.

“Existing phase diagrams are based on experimental data that are difficult to obtain and often inaccurate, especially at low temperatures, where material transformations are extremely slow,” explained Dr. Chenying Shi, lead author of the publication.

“This new method overcomes these barriers by eliminating the need for this experimental data,” added the Marie Skłodowska-Curie Actions postdoctoral researcher.

Instead of relying on experimental measurements, the researchers used first-principles and statistical mechanics-based simulations to calculate the energy of different atomic configurations, including the effects of atomic vibrations and magnetic properties.

The results provide a more accurate understanding of the stability of the different phases in this alloy system. The new phase diagram shows significant differences compared to currently accepted models, correcting the boundaries between the different crystalline structures (fcc and hcp).

The study also reveals that atomic lattice vibrations, known as vibrational entropy, play a crucial role in the stability of these phases, while magnetism has a limited impact on transitions at lower temperatures.

“This method allows us to observe, with an unprecedented level of detail, how atoms are arranged in these alloys and why,” said Dr Shi.

“This level of precision is essential for designing the next generation of high-performance materials more rapidly and efficiently.”

The research team also included Prof. Javier LLorca, Scientific Director of IMDEA Materials and Full Professor at the UPM, and Dr. Wei Shao, former researcher at the institute.

The researchers anticipate that this methodology could be applied to more complex systems, such as Ni-Co-Cr-based high-entropy alloys, accelerating the development of a new generation of superalloys for applications under extreme conditions.

This research was carried out as part of the Horizon MSCA PD-MPEA project funded by the European Union under Grant Agreement 101148301. Views and opinions expressed are, however, those of the author(s) only and do not necessarily reflect those of the European Union. Neither the European Union nor the granting authority can be held responsible for them.