Additive manufacturing of high entropy alloys: A practical review

The novel idea of alloying, which is based on the utilization of multiple principal elements in high concentrations, has created a novel class of promising materials called high entropy alloys(HEAs). So far, several HEAs with outstanding properties beyond those of conventional alloys have been discovered, and new superior high-entropy alloys are still expected to be developed in the future. However, the fabrication process of HEAs through conventional manufacturing techniques suffers from significant limitations due to the intrinsic requirements of HEAs. Additive manufacturing(AM), on the other hand, has provided new opportunities for fabricating geometrically complex HEAs with the possibility of in situ tailoring of their microstructure features. Considering the growing interest in AM of HEAs during most recent years, this review article aims at providing the state of the art in AM of HEAs. It describes the feedstock requirements for laser based AM techniques. Thereafter, a comprehensive picture of the current state of nearly all HEAs processed by laser metal deposition(LMD), selective laser melting(SLM) and selective electron beam melting(SEBM) is presented. Special attention is paid to the features of AM derived microstructures along with their outstanding properties and underlying mechanisms for various material processing combinations. The AM of interstitial solute hardening HEAs, HEA matrix composites as well as non-beam based AM of HEAs will also be addressed. The post-AM treatments and the strategies to fabricate defect-free HEAs are summarized. Finally, a conclusion of current state and future prospects of additive manufacturing of HEAs will be presented.