How high-entropy alloys could offer new circular economy future

And research programs out of IFM are taking the development of high-entropy alloys even further – finding new ways to not only improve its production and application but move the high-performance alloy into a circular economy. 

Traditionally, the mainstream strategy for alloys production is to pick one element as the solvent and add lesser amounts of alloying elements as solutes to tailor properties toward desired directions. Alloys are named after their principal constituent, for example ferrous alloys, aluminium alloys, titanium alloys and nickel alloys.

High-entropy alloys or multi-component alloys are a family of alloys designed with a completely new strategy, by using five or more principal elements in equal or near-equal concentrations. 

Associate research fellow Dr Jithin Joseph was the first researcher at IFM to start work on the high entropy alloy system with the support of Associate Professor Daniel Fabijanic and Professor Peter Hodgson. Since then, other researchers from the IFM metals group have joined him in extending their knowledge of conventional alloys to this new alloy system.

‘The concept of high-entropy alloys has attracted world-wide attention for its design of novel metallic materials largely sparked by the enormous possibilities in compositions, microstructures, and properties,’ Dr Joseph says.

‘There are still research challenges that we face with this alloy system. The multi-dimensional compositional space that can be tackled with this approach is practically limitless and identifying regions within this space where high-entropy alloys with potentially interesting properties remains a challenge.’

Despite the challenges, to date the IFM team’s research has shown enormous promise. 

‘Our research group under the supervision of Professor Matthew Barnett and Associate Professor Daniel Fabijanic used a high entropy alloy design concept to find new paradigms in alloy science that make it easier to recycle and reuse high performance metal alloys to maximise value from end-of-life materials,’ he says.

‘Rather than selling Australian scrap alloy overseas, we will look for domestic recycling opportunities, and in the process, save up to 95 per cent of the energy costs required to manufacture new metal – the theme of Professor Barnett’s ARC Laureate Fellowship. 

‘This research will contribute to developing a 21st century circular economy, creating breakthrough innovations to benefit Australia’s metal fabrication and scrap metal sectors, while also providing Australia with important sovereign capability. 

‘Professor Barnett’s idea was to make use of all the scrap alloys. There is no need to export it outside of Australia when we can make full use of this scrap here in Australia.’

Dr Joseph says their scrap tolerant alloy design concept produces extraordinarily broad compositionally flexible alloys into which they could essentially ‘chuck in’ unsorted mixes of scrap metal as proposed by Professor Barnett, and still meet the required properties.

‘We proposed a compositionally flexible alloy that has the capability to accept input from varying co-mingled flows of end-of-life alloys,’ he says. 
 ‘The concept was motivated by the surprising number of high entropy alloys reported in the literature that display a similarity of properties despite their wide dispersion of composition. 

‘We used the Machine Learning technique – Bayesian Optimization– to search for compositions that display structural performance criteria (plastic and elastic responses) that fall within specified limits. 

‘A practical solution to the challenge of specifying compositionally flexible alloys is to provide variant exemplars based on the end-of-life alloys from which the alloy could conceivably be made.

‘For example, we ran 37 common Ni alloys through our performance predictor for different additions of stainless steel grade 316. 

‘This case study successfully demonstrated an avenue for value creation from end-of-use materials out of high-end specialty alloys where costs of separating co-mingled alloy flows are prohibitively high, such as superalloys with relatively lower tonnage of scrap metal availability. 

‘This research was published as a featured article in the prestigious ‘Acta Materialia’ journal by Elsevier publications.’

The work follows on from IFM metals group’s four-year research program “New 3D printed high entropy alloys for exceptional performance in aerospace and mining” which is now ready to be applied to industry. 

Funded by the India-Australian Strategic Research Fund by the Federal Department of Innovation, Industry, Science & Research, IFM researchers teamed up with the Indian Institutes of Technology, the Indian Institute of Science, Monash University, RMIT and General Electric Research to develop high entropy alloys for high-temperature applications. 

‘The laboratory scale tests at IFM showed the exceptional wear resistance, oxidation resistance and strength at high operating temperatures on par with conventional high-temperature coatings and structural alloys, such as superalloys,’ Dr Joseph says.

‘We are working towards the industry-scale testing of these compositions to employ them for practical applications. 

‘The collaboration with the research group of Professor Svetha Venkatesh from Applied Artificial Intelligence Institute aided us in the exploration of the huge compositional space using computational/machine learning techniques and the characterisation and comprehension of their mechanical behaviour from fundamental and practical perspectives.’

Dr Joseph says the team continues to collaborate with various industries on specific-, process and product-oriented innovative ideas and turn them into sustainable, economical solutions, from alloy design to process optimisation. 

Ongoing research work includes the IFM’s Steel Research Hub research team working with Infrabuild Wire and InfraBuild Manufacturing to deliver advancements across both wire and reinforcing products. InfraBuild’s new Viribar™ 750 high-strength steel fitments resulted in a 25 to 33 per cent reduction in carbon emissions per tonne of fitments in a recent residential build contracted to structural engineering firm SCP Consulting.

Dr Joseph in his first postdoctoral research under the supervision of Associate Professor Daniel Fabijanic and Professor Minoo Naebe is also working with Australia’s leading automotive brake manufacturer Bendix Ballarat’s research and development department. Together they are developing automotive brake pads with minimal environmental impact that ensure low particle emissions when braking to achieve cleaner wheels and longer disc brake rotor life. 

‘Different industries in Australia have adopted circular economy approaches in their processes,’ Dr Joseph says.

‘A large proportion of Australia’s circular economy practices is focused on metal reuse and recycling. 

‘The desire to create high-performance alloys and technological solutions using processes and innovations that are sustainable explains why a vast number of circular economy publications in the country focus on the metallic industries. 

‘The industry partners I worked with have shown the drive to go circular with prime importance to environmental sustainability along with economic growth or green economy. The road to a circular economy is not a smooth ride and the technical requirements and barriers were different across individual partners. 

‘But we are committed to meet the rising demand for technological advancements that complement a circular economy.’

This Real-world Impact article featured in IFM’s 2021 Annual Report. Read the full annual report, here