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

Abstract

Anisotropic microstructure and mechanical properties are vital considerations in the practical applications of 3D-printed 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° 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° and 90° samples. The post-mortem microscopic analysis indicates that this ductility anisotropy primarily originates from the crack propagation behavior. In the 0° 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° and 90° samples, leading to the straight crack propagation path along the MPBs and therefore reduced ductility.