Anisotropy in 3D-printed (FeCoNi)86Al7Ti7 high entropy alloy

Anisotropic microstructure and mechanical properties are vital considerations in the practical applications of 3Dprinted metallic materials; however, limited attention has been given to the anisotropy in 3D-printed high entropy alloys (HEAs). This study systematically explores the structural and mechanical anisotropy of (FeCoNi)86Al7Ti7 HEA with low porosity, fabricated via selective laser melting (SLM). The SLM process, characterized by directional and repeated thermal dissipation, creates an anisotropic structure consisting of epitaxial columnar grains aligned parallel to the building direction, subsequently influencing mechanical anisotropy. Tensile testing unveils slight anisotropy in strength but significant differences in ductility for the SLMed HEA. The 0 degrees sample demonstrates the optimal combination of strength and plasticity, boasting a tensile elongation of 31.5 %, approximately 2.6 times higher than that of the 45 degrees and 90 degrees samples. The post-mortem microscopic analysis indicates that this ductility anisotropy primarily originates from the crack propagation behavior. In the 0 degrees sample, crack propagation occurs through both intergranular and transgranular modes, with the robust interactions between the two modes providing an obstruction to crack propagation. On the contrary, crack widening occurs essentially along the continuous melting pool boundaries (MPBs) in 45 degrees and 90 degrees samples, leading to the straight crack propagation path along the MPBs and therefore reduced ductility.

Automated summary

This study systematically explores the structural and mechanical anisotropy of 3D-printed high entropy alloys. The results show that the selective laser melting (SLM) process creates an anisotropic structure, which influences the mechanical properties. The 0 degrees sample exhibits the optimal combination of strength and plasticity, while the 45 degrees and 90 degrees samples have reduced ductility.