Design, microstructure, and mechanical property of negative Poisson's ratio porous structure fabricated by LPBF of AlCoCrFeNi2.1 eutectic high-entropy-alloy

Abstract

Negative Poisson's ratio (NPR) materials are a type of structural materials that show an atypical deformation response. In general, metal-based porous materials with NPR do not have good mechanical properties due to the substrate's limited yield strength and plasticity, as the NPR behavior is unlikely to play a continuous role in the deformation. AlCoCrFeNi2.1, a eutectic high-entropy alloy (EHEA) with high yield strength and high ductility was used to fabricate the NPR structures by laser powder bed fusion (LPBF) to enhance the structures mechanical properties and NPR behavior. Structures with four different sets of structural parameters were designed for this study. The microstructure and mechanical properties of AlCoCrFeNi2.1 EHEA, synthesized by LPBF were studied, and the strength and energy absorption effect of NPR porous structure materials were investigated by static and dynamic compression experiments. Research showed the large number of inter-phase interfaces provided by the nano-scale cellular eutectic microstructure effectively restrict dislocation movement, thereby enhancing the strength and toughness of this EHEA alloy, endowing it with superior impact resistance, fracture resistance, and mechanical energy absorption. The compressive performance and the mechanical energy absorption capacity of the 3D EHEA-based NPR porous structure strongly depend on the inclination angle Ф between the thick rod and the horizontal direction in the 2D single-body model design. The strength and energy absorption of the structure with a high inclination angle of 75° material are both higher than those of the structure with a low inclination angle of 45° by almost a factor of two.