Abstract:

Additive manufacturing (AM), particularly laser powder bed fusion (LPBF), has revolutionized the fabrication of high-performance metal components for aerospace by enabling more complex geometries to be produced with superior mechanical properties and minimal material waste [1-5]. High-strength Ni-based superalloys like Inconel 718 (IN718) are especially compatible with LPBF due to their weldability and are already widely used in aerospace [6], [7]. Lattice structures, especially strut-based architectures, have gained attention for their excellent strength-to-weight ratios and energy absorption capabilities [8-11]. This study investigates high-entropy lattice structures (HELS), which combine multiple unit cell types in spatially heterogeneous arrangements inspired by the atomic disorder of high-entropy alloys (HEAs). By fabricating IN718 lattices with hybrid topology and microstructural variation (aging heat treatment to enhance precipitation of γ″ strengthening phases), this work explores the coupled influence of lattice architecture and material microstructure on mechanical performance, contributing to the development of advanced damage-tolerant metamaterials for aerospace applications.
The study evaluates the room temperature compressive mechanical behavior of 70 hybrid lattice structures composed of different combinations of body-centered cubic (BCC), face-centered cubic (FCC), octet truss (OT), and simple cubic (SC) unit cells, mixed using either random (R) or special quasi-random structure (SQS) strategies. These lattices were tested in both as-built (AB) and peak-aged (PA) conditions to assess not only the effects of architectural entropy, but also how the γ″ precipitation influences mechanical performance. In the AB condition, hybridization significantly improved yield strength, energy absorption, compared to rule-of-mixtures (ROM) predictions and enhanced the deformation stability. SQS-mixed lattices often outperformed their randomly mixed counterparts by reducing clustering of similar unit cells, thereby suppressing strain localization and stress drops after yielding. After aging, all lattices exhibited higher strength and energy absorption than both the AB lattices (at the cost of reduced ductility) and ROM predictions. However, the influence of mixing strategy was less consistent compared to the AB lattices, perhaps due to the more dominant role of local stress concentrations due to precipitation in the PA lattices.
Simulation and experimental observations confirmed that failure in the as-built condition typically initiates at clusters of the same unit cells, regardless of microstructure and topology. This effect is minimized by the SQS approach since it is designed to generate fewer clusters of similar cells. Under the peak-aged condition, microstructural effects outweigh the influence of mixing strategy on the mechanical performance of these lattice structures. These findings illustrate the importance of both architecturally optimized designs and microstructure in the resulting mechanical behavior. This study also suggests that the introduction of architectural disorder may be an effective way to design high-performance aerospace materials.