Effects of a modified heat treatment on the quasi-static and dynamic behavior of additively manufactured lattice structures

Abstract

The exibility of additive manufacturing techniques that produce parts from powders layer-by-layer directly from a digital model, enabled the fabrication of complex lightweight lattice structures with precisely engineered mechanical properties. Herein, an investigation of the quasi-static and dynamic behavior of additively manufactured (AM) triply periodic minimal surface (TPMS) lattice structures before and after a novel post-process heat treatment step is conducted. The specimens were fabricated out of Inconel 718, a nickel-chromium-based superalloy, using a selective laser melting technique with three different topologies, namely, Gyroid, Primitive, and I-WP. The quasi-static tests were conducted at a strain rate of 0.002 s − 1 and dynamic experiments were conducted using a split Hopkinson pressure bar at three different strain rates, 600 s − 1 , 800 s − 1 , and 1000 s − 1 . It was shown that while the strain rate does not signi cantly affect the mechanical responses of the lattice structures, the heat treatment step dramatically changes their behavior. Results demonstrated that after the heat treatment, the yield strength of the I-WP specimens increased by 65.2% under a quasi-static load. Also, ow stress after yielding in the dynamic tests was shown to increase around 9.6% for I-WP specimens and up to 12.8% for Gyroid specimens. The speci c energy absorption values were 10.5, 19.1, and 10.7 for I-WP, Gyroid, and Primitive, respectively, before the heat treatment, and changed to 19.6, 19.8, and 15.4 after the heat treatment. The results con rm that by precisely designing the architecture of a lattice structure and implementing a modi ed heat treatment process, it is possible to optimize the weight, strength, and energy absorption capability of this type of metamaterial.