Composition inhomogeneity reduces cracking susceptibility in additively manufactured AlCoCrFeNi2.1 eutectic high-entropy alloy produced by laser powder bed fusion

Pre-alloyed and blended powders are frequently used feedstock options for additive manufacturing; however, nanoscale compositional inhomogeneities induced by blended powders are often ignored. This composition inhomogeneity is more pronounced in eutectic high-entropy alloys (HEAs) with small solidification ranges and sluggish diffusion effects. In this study, AlCoCrFeNi2.1 eutectic HEAs were prepared by laser powder bed fusion (LPBF) using both pre-alloyed and blended powders. The alloy built using the pre-alloyed powder (PA) exhibited cellular structures that consisted of ordered body-centered cubic (B2) cells decorated with face-centered cubic (FCC) networks. The composition inhomogeneity in the alloy built using blended powders (BP) led to lamellar structures consisting of alternate FCC and B2 lamellas. The orientation relationships between FCC and B2 in both PA and BP were determined as {110}(B2)//{100}(FCC), < 001 >(B2)//< 011 >(FCC). The fine cellular structures in PA resulted in high ultimate strength (1400 MPa) but poor ductility. Solid-state cracking and delay cracking were observed in PA. The straight and extended FCC lamella in BP provided preferential channels and long distances for dislocation slippages, which combined high strength (1200 MPa) and ductility (10%). The improved deformation ability of BP enabled a strain-tolerant microstructure and eliminated the solid-state and delay cracking in as-built LPBF AlCoCrFeNi2.1 alloys.