AlxCoCrFeNi high entropy alloys from metal scrap: Microstructure and mechanical properties

The more alloys we can make from metal scrap, the better. The present paper examines the prospect of making high entropy alloys (HEA) completely from existing commercial alloys. Three HEAs were fabricated from pure elemental billets and from scrap ingots with two different levels of impurities (2 wt% and 9 wt%): a Al0.3CoCrFeNi alloy with a single-phase FCC structure, a Al0.6CoCrFeNi alloy with a multi-phase FCC/BCC structure and a Al0.9CoCrFeNi alloy with a spinodal BCC/B2 structure. The effect of various impurity levels on the microstructure and mechanical properties was analysed and compared to the commercially pure HEAs in the as-cast and homogenised heat-treated conditions. The HEAs with low impurities (2 wt%) exhibited microstructural features and mechanical properties similar to that of the commercially pure HEAs. On the other hand, the HEAs with high levels of impurities (9 wt%) exhibited high strength and reduced plasticity which resulted from the refined grain structure and the precipitation of hard phases (such as Laves and carbides). This strategy shows the potential to eliminate or reduce high-cost raw materials for the fabrication of HEAs with a refined microstructure and improved mechanical properties by suitably selecting the scrap ingot streams.