Going beyond steel: Exploring the processing of ever more complex and higher melting temperature alloys

In our continuous efforts to extend OCAS’s alloy production capabilities within our Metal Processing Centre, we cast, process and characterise small quantities of Nb alloys as well as various High Entropy Alloys. Thus, demonstrating that OCAS is the place to be when looking for metals for R&D purposes.

The high-entropy alloy concept is based on the idea that high mixing entropy can promote the formation of stable singlephase microstructures. In more recent years, the concept has been broadened to ‘compositionally complex alloys’, with combinations of a minimum of 3 elements in ranges of 5% to 35%. These compositionally complex alloys can offer an infinite pool of new alloys with unexplored properties. Our unique experimental high-throughput flow methodology enables OCAS to rapidly screen high numbers of formulations. This is exactly what OCAS is putting into practice in the Horizon Europe project FORGE.

SCREENING OF COMPOSITIONALLY COMPLEX ALLOYS: PAVING THE WAY FOR MACHINE LEARNING

The FORGE consortium aims to develop a set of cost-effective highly protective coatings, based on novel compositionally complex materials – both metal alloys and ceramics – to provide the required hardness, chemical stability and gas barrier properties for challenging applications. OCAS’s role in this project is to perform a first screening of the compositionally complex alloys. By pioneering unknown alloy processing at lab-scale, OCAS is making it possible to gather enough data to train and feed the machine learning model. Although OCAS has a long tradition in induction melting and casting ferrous and several non-ferrous alloys, melting compositionally complex alloys adds to the challenge. In fact, elements are not only present in large quantities in compositionally complex alloys but several of them have high (e.g. Ti, Cr & V) to very high (Nb, Mo, Ta & W) melting points. In addition, these elements can be very reactive to most crucibles. To avoid timeconsuming iterations in a high-throughput flow, anticipating the selection of raw

Expanding towards high melting metals and compositionally complex alloys not only enlarges our offer towards customers, it is also exciting to enter such new fields of metallurgy.

Nele Van Steenberge & Michal Mroz

materials or pre-alloys and crucibles is crucial. OCAS has already synthetised over 30 compositionally complex alloys, allowing the measured hardness to be compared to the machine learning model predictions. Despite the huge number of available hardness values in literature for high entropy alloys and compositionally complex alloys, the need for a fast way to provide experimental data remains to support databases and machine learning models. OCAS is perfectly positioned to cover this need.

UPSCALING HIGH ENTROPY ALLOY PRODUCTION – CANTOR’S ALLOY CASTING

Thanks to their exceptional properties, high entropy alloys and compositionally complex materials attract attention from both industry and research. Academic research has largely remained limited to small volume synthesis techniques. To commercialise these alloys, upscaling is necessary. OCAS has successfully cast a 100kg homogeneous Cantor’s CoCrFeMnNi high entropy alloy via vacuum induction melting. First processing and characterisation have produced good results, and a more detailed analysis is ongoing.