Considering sustainability when searching for new high entropy alloys

Abstract

Alloying elements bring with them a level of undesirable societal impact. The present paper examines this impact, in terms of primary production, for 340 newly proposed high entropy compositions. Three areas of sustainability are considered: economic viability, environmental impact and human well-being. The high entropy alloys are considered in two classes: body centred cubic and related alloys with potential for high temperature application and face centred cubic and related Cantor-type alloys. The former are compared to Ni-based superalloys and the latter to advanced steels. It is seen that with improved performance of Ni-based superalloys there has been an increase in undesirable impact across many of the indicators we employ. However, some recently proposed high temperature high entropy alloys – especially Yeh-type High Entropy Superalloys - display notably lower levels of undesirable impact than Ni-based superalloy compositions. Cantor-type face centred cubic alloys, however, do not compare so favourably when stacked up against the best steels, for room temperature strength and ductility. We show that, in general, there is good scope for high entropy alloys to be designed that target lower levels of undesirable impact.