Mechanical Properties of Diamond‐Structured Polymer Microlattices Coated with the Silicon Nitride Film

Abstract

Inspired by crystal structures of the diamond and polymer/ceramic core-shell structures of hard biological materials, diamond-structured polymer/SiN microlattices with enhanced mechanical properties have been fabricated by 3D printing and plasma enhanced chemical vapor deposition method. It is found that the compressive strength of the resultant microlattices improves with increasing silicon nitride film thickness and can reach 1.95 MPa at the thickness of 400 nm, which is 3.4 times higher than the pure polymer, but a little increase of 4.8% in density, which is only 169.2 kg m À3 . The work may provide a simplified and feasible avenue to improve the strength of low density materials.Lightweight cellular materials have wide applications in fields of aerospace, transportation, and architecture, due to their unique properties such as acoustic absorption, [1,2] energy absorption, [3] thermal insulation, [4] and shock or vibration damping. [5] Human have created numerous lightweight cellular materials, including honeycombs, [6,7] aerogels, [8][9][10] foams, [11][12][13][14][15] microlattices. [16] Microlattices are a new class of cellular materials possessing lower density and better mechanical performance than traditional random foams, because of the order and periodicity in structure. There have been many studies on microlattices with different constituent, like polymer, [17,18] metal, [19][20][21] ceramic, [22][23][24][25] and graphene. [26] The structure of lattices is formed by repeating a unit cell with specific geometry periodically in three dimensions, so, the density and mechanical performance of the lattices depend strongly on the cell geometry including shape, size, and structural hierarchy. [27][28][29] Among common topologies used to produce structure materials, the diamond structure is preferred for attaining high strength and lower density materials for its special configuration, which exhibits high spatial symmetry and strong stability to resist deformation. [30][31][32] The strength of lattice materials is determined not only by the architecture but also by the constituent materials. Among numerous engineering materials, ceramics have the highest strength and stiffness. Furthermore, silicon nitride is one of the materials with highest hardness in nature, which belongs to atomic crystal. However, ceramics are limited for applications because of their brittleness. During the process of hundreds of million years of evolution, nature has already developed the ability to turn brittleness into toughness by combining ceramic and organic matter into hybrid composites, which exhibit much enhanced strength in comparison to their constituents. [33,34] Examples include wood, [1] bone, [35,36] sponge, [37] nacre, [38] crustaceans, and exoskeleton of arthropods. [39,40] As a typical example, crustacean cuticle was formed from a chitin-protein organic template, mineralized by calcium phosphate and calcium carbonate, resulting a composite structure comprised of organic core and inorganic shell, whose stiffness (>5 G...

High‐Entropy Alloy (HEA)‐Coated Nanolattice Structures and Their Mechanical Properties

“…[43] It is worth mentioning that the composite nanolattices exhibit superior compressive strain, which possibly due to the polymeric core supporting. Finally, through these data, it can be calculated that the specific compressive strength of the presented composite nanolattices is 0.032 MPa kg À1 m 3 , which is comparable even higher than that of the micro/nano lattice reported before, for instance, polymer/NiB (0.017 MPa kg À1 m 3 ), [41] polymer/Si 3 N 4 (0.012 MPa kg À1 m 3 ), [42] and SiC microlattices (%0.023 MPa kg À1 m 3 ) [44] and a detailed comparison can be found in Table S1, demonstrating the superior mechanical properties of the composite nanolattices based on the synergistic effect between polymer and HEA film. Thin films, both amorphous and crystalline films, have been extensively reported to be capable of enhancing the performance of many types of materials through coating, especially the mechanical performance of substrate materials.…”

“…However, when the core is not still enough to increase the compressive capability and the buckling stress is dominated by the buckling stress of the shell. [42] Meanwhile, the HEA is in the ductile-to brittle transition due to the size effects. [41] Therefore, a brittle behavior would be observed at a certain point, which is in good agreement with other reports.…”

“…[41] Therefore, a brittle behavior would be observed at a certain point, which is in good agreement with other reports. [12,41,42] To demonstrate the important role of the polymer core in the composite nanolattices, a loading-unloading compression test was employed ( Figure S4). As shown in the exhibited mechanical behaviors, nearly the same Young's modulus (74.5 AE 3.5 MPa) was observed, indicating the superior recoverability of the composite nanolattices under an applied strain of nearly 8%.…”

“…[1][2][3][4][5][6][7][8][9] The strength of lattices is determined not only by the order and periodicity of its structure, but also by the constituent materials. [10,11] Recently, numerous engineering materials such as Al 2 O 3, [12][13][14] Ni-P alloy, [4,15] glassy carbon, [16] copper, [17] gold, [18] and metallic glass [19,20] have been employed as constituent materials to significantly enhance the mechanical properties of pristine polymer scaffolds with respect to its strength and stiffness. Nevertheless, exploring a kind of lightweight, low-cost, and easily fabricated material with promising mechanical features that are easily to be coupled with pristine lattice structure is still a challenge.…”

Mechanical Metamaterials and Their Engineering Applications

“…However, the structures typically exhibit stable cyclic behavior subsequently . This mechanism is also responsible for the layer‐by‐layer deformation in a lot of lattice materials, which allows controlled dissipation of energy …”