Above the insulating atmosphere of the Earth, satellites and spacecraft encounter very harsh environments of extreme heat or cold and damaging radiation. Advanced materials and associated manufacturing processes are required for the long-term integrity of space systems and the safety of astronauts. Given the practically infinite variety of materials, the power of computational modelling is critical to development. The EU-funded ICARUS project developed the numerical tools to design thermodynamically stable nanocrystalline metal alloys and demonstrated their utility in selected materials of interest to aerospace applications.
Stabilising the nanocrystalline structure of the alloys
Alloys, metallic substances made of two or more elements, are widely used in the aerospace industry to integrate the best properties of individual metals. Coarsening, intuitively like the production of larger coarser grains (crystallites or tiny crystals) leading to larger pores in between the grains, is an important consideration when using nanocrystalline alloys. Grain boundaries are key to coarsening by increasing the excess Gibbs free energy (G) of the system. Grain growth is a consequence of the thermodynamic driving force to reduce this excess. Thermodynamic stabilisation eliminates the driving force, and thus grain growth and coarsening, through appropriate selection of alloys.
High-throughput screening zeroes in on the best candidates
While thermodynamic stabilisation is simple in concept, project coordinator Nicolas A. Cordero illustrates its complexity in practice: “Consider the case of binary alloys (made of two elements). If we select just 10 interesting majority elements and 5 interesting minority elements, we have 50 possible combinations. If we want to investigate 10 different percentage compositions and test their thermal stability at 10 temperatures for each of them, we end up with 5 000 systems and conditions to be experimentally investigated!” ICARUS developed a high-throughput screening tool to solve this problem. Overcoming the challenges of combining classical and statistical thermodynamics, ICARUS delivered a unified model enabling the exploration of the Gibbs free energy surface. It can identify thermodynamically stable nanocrystalline alloys based on known physical and chemical data. Fabrication of candidate specimens enabled validation of the model as well as improvement of current techniques for nanocrystalline powder creation and the sintering of solid pieces.
ICARUS’ innovation takes flight
ICARUS’ high-throughput screening tool will enable engineers to deliver nanocrystalline alloys satisfying important goals of the Advisory Council for Aviation Research and Innovation in Europe. These include enhanced radiation resistance via self-healing mechanisms, enhanced thermal resistance thanks to high heat conduction and low thermal expansion, and, lastly, high mechanical strength combining low weight with high performance for lower fuel consumption. Outcomes are being distributed in numerous ways including through social media pages. videos, leaflets and posters, and newsletters as well as two workshops, participation in a number of scientific conferences, and open-access scientific publications. Cordero summarises: “ICARUS delivered computational tools that can predict the thermal stability of nanostructured alloys, providing a practical way to screen suitable alloys for experimental testing. Only this interplay of theory and experiment can produce the innovative materials required of present and future space applications.” A parallel project, ICARUS-SW, is now underway to pave the way for exploitation of the ICARUS code.
ICARUS, alloys, nanocrystalline, thermal, coarsening, grain, aerospace, thermodynamic, computational, high-throughput screening, Gibbs free energy, radiation, space, sintering, powder