Post-processing of additively manufactured high-entropy alloys - A review

Additive manufacturing of high-entropy alloys (HEAs) might lead to defects in the as-built condition such as porosity, residual stresses, elemental segregation, lack of fusion, and inhomogeneous microstructure. As a result, the post-processing of parts fabricated by the powder bed fusion (PBF) and directed energy deposition (DED) processes is sometimes required to improve the mechanical and functional properties. Accordingly, the heat treatment of additively manufactured HEAs is reviewed in this article, including (I) hot isostatic pressing (HIP) for closure of pores and cracks, (II) annealing/solutionizing treatment for dissolution of unwanted phases, formation of equiaxed grain structure by recrystallization, and reduction of the segregation effects, (III) aging treatment for formation of desired precipitates and/or phases, and (IV) deep cryogenic treatment (DCT) for microstructural refinement, inducing compressive residual stresses, and phase transformation. Moreover, important suggestions for future works are proposed, including the investigation of the effects of special alloying elements, consideration of lightweight/refractory/compositionally graded HEAs, and implementation of metal additive manufacturing processes based on the friction stir processing (FSP) technology.