Effects of inter-layer remelting frequency on the microstructure evolution and mechanical properties of equimolar CoCrFeNiMn high entropy alloys during in-situ powder-bed arc additive manufacturing (PBAAM) process

An equiatomic CoCrFeNiMn High Entropy Alloy (HEA) was in-situ deposited by the powder-bed arc additive manufacturing (PBAAM) process for the first time. Comparative research was conducted on the evolution of phase, crystallographic orientation, dislocation morphology, precipitation, and mechanical performance with the accumulation of inter-layer remelting times. The experimental outcomes manifested that the PBAAMed CoCrFeNiMn HEA consists of a stable solid-solution FCC structure, with decreased lattice parameter but slightly increased (full width at half maximum) FWHM as the accumulation of the inter-layer remelting. The {001}<100> cube texture with a weakened texture intensity was detected with an increment of inter-layer remelting frequency from once to 5 times, yet it was transformed into {011}<100> Goss texture with a further increase to 7 times. Additionally, the mean grain diameter distinctly decreased, while the volume fraction of (low angle grain boundaries) LAGBs and dislocation density remarkably added up as the accumulated inter-layer remelts. Predominant cellular substructure generated in all process conditions and could be easily differentiated by elemental segregation. Both the σ and M23C6 Cr-rich precipitates in nano-scale and submicron MnS precipitate were detected on the grain boundaries of the PBAAMed deposited components, with a rather sparse distribution. Speaking of mechanical performance, the YS, UTS, and hardening rate are generally increased while the UE is gradually decreased as increased inter-layer remelting times. The studied PBAAMed CoCrFeNiMn HEA possesses comparable mechanical performances with the counterparts of laser-deposited and as-cast ones. The strengthening mechanisms of the studied material are predominantly the grain boundary strengthening and dislocation strengthening. This investigation would be a valuable resource in the research field of fabricating HEA alloys with acceptable microstructure and properties using the PBAAM method.