Simultaneously healing cracks and strengthening additively manufactured Co34Cr32Ni27Al4Ti3 high-entropy alloy by utilizing Fe-based metallic glasses as a glue

Abstract

Solidification cracking issues during additive manufacturing (AM) severely prevent the rapid development and broad application of this method. In this work, a representative Co34Cr32Ni27Al4Ti3 high-entropy alloy (HEA) susceptible to crack formation was fabricated by selective laser melting (SLM). As expected, many macroscopic cracks appeared. The crack issues were successfully solved after introducing a certain amount of Fe-based metallic glass (MG) powder as a glue during SLM. The effect of MG addition on the formation and distribution of defects in the SLM-processed HEA was quantitatively investigated. With an increasing mass fraction of the MG, the dominant defects transformed from cracks to lack of fusion (LOF) defects and finally disappeared. Intriguingly, the MG preferred to be segregated to the boundaries of the molten pool. Moreover, the coarse columnar crystals gradually transformed into equiaxed crystals in the molten pool and fine-equiaxed crystals at the edge of the molten pool, inhibiting the initiation of cracks and providing extra grain boundary strengthening. Furthermore, multiple precipitates are formed at the boundaries of cellular structures, which contribute significantly to strengthening. Compared to the brittle SLM-processed Co34Cr32Ni27Al4Ti3 HEA, the SLM-processed HEA composite exhibited a high ultimate tensile strength greater than 1.4 Ga and enhanced elongation. This work demonstrates that adding Fe-based MG powders as glues into SLM-processed HEAs may be an attractive method to heal cracks and simultaneously enhance the mechanical properties of additively manufactured products.