Sustainability of High Entropy Alloys and Do They Have a Place in a Circular Economy?

Abstract Ideally, new materials should foster sustainability. How to apply this to high entropy alloys (HEAs) is the subject of the present overview. We show HEAs have a number of potential applications in sustainable technologies. They may also slot sustainably into a circular economy, if they can mediate a lowering of the life cycle energy rate. This term forecasts the rate of energy expenditure over the life cycle of a replaceable component. The energy cost of high entropy alloy production, and the challenges they will present to recycling, may be justified from a sustainability perspective, so long as they can mediate sufficient sustainability benefits in their use phase. Promising applications include functional roles in energy production and storage and applications in gas turbines. Although high entropy alloys are most likely to be downcycled at the end of their lives, there is a growing body of literature pointing to interesting ways high entropy alloys might be produced from recycled metal flows, thereby opening up avenues to significantly lower their energy cost of production. Evidence is also presented for a possible 5th core effect in High Entropy Alloys, whereby the presence of multiple alloying additions serves to stabilize the properties against variation in composition. This effect may facilitate their production using scrap metal. The greater the co-ordination between alloy design, component design, and manufacturing innovation, the more likely HEAs will prove to be a sustainable step forward.