Optimizing film thickness to delay strut fracture in high-entropy alloy composite microlattices

Incorporating high-entropy alloys(HEAs) in composite microlattice structures yields superior mechanical performance and desirable functional properties compared to conventional metallic lattices. However, the modulus mismatch and relatively poor adhesion between the soft polymer core and stiff metallic film coating often results in film delamination and brittle strut fracture at relatively low strain levels(typically below 10%). In this work, we demonstrate that optimizing the HEA film thickness of a CoCrNiFe-coated microlattice completely suppresses delamination,significantly delays the onset of strut fracture(~100% increase in compressive strain),and increases the specific strength by up to 50%. This work presents an efficient strategy to improve the properties of metal-composite mechanical metamaterials for structural applications.

Accuracy controlling and mechanical behaviors of precursor-derived ceramic SiOC microlattices by projection micro stereolithography(PμSL)3D printing

Precursor-derived ceramic SiOC(PDC-SiOC)microlattices exhibit excellent oxidation resistance,high-temperature stability,and superior mechanical properties.However,the printing accuracy of the PDC-SiOC microlattices by 3D printing is still limited,and mechanical properties of the PDC-SiOC microlattices have not been studied systematically.Here,PDC-SiOC octet microlattices were fabricated by projection micro stereolithography(PμSL)3D printing,and photoabsorber(Sudan III)’s effect on the accuracy was systematically analyzed.The results showed that the addition of Sudan III improved the printing accuracy significantly.Then,the ceramization process of the green body was analyzed in detail.The order of the green body decreased,and most of their chemical bonds were broken during pyrolysis.After that,the PDC-SiOC microlattices with different truss diameters in the range of 52–220μm were fabricated,and their mechanical properties were investigated.The PDC-SiOC microlattices with a truss diameter of 52μm exhibited higher compression strength(31 MPa)than those with bigger truss diameters.The size effect among the PDC-SiOC microlattices was analyzed.Our work provides a deeper insight into the manufacturing of PDC-SiOC micro-scaled architectures by 3D printing and paves a path to the research of the size effect in ceramic structures.

Fabrication and Characterization of Graphene-Enhanced Hollow Microlattice Materials

A method was developed and proposed to fabricate graphene-enhanced hollow microlattice materials,which include the three-dimensional(3D)printing,nanocomposite electroless plating,and polymer etching technologies.The surface morphology and uniformity of as-deposited coatings were systematically characterized and analyzed.Moreover,the mechanical properties of the microlattices were investigated through quasi-static compression tests.The results demonstrated that a uniform Nickel-phossphorous-graphene(Ni-P-G)coating was obtained successfully,and the specific modulus and strength were increased by adding graphene into the microlattice materials.The optimal mass concentration of graphene nanoplatelets was obtained after comparing the specific modulus and strength of the materials with different densities of graphene,and the strength mechanism was discussed.

Tailoring mechanical properties of PμSL 3D-printed structures via size effect

Projection micro stereolithography(PμSL)has emerged as a powerful three-dimensional(3D)printing technique for manufacturing polymer structures with micron-scale high resolution at high printing speed,which enables the production of customized 3D microlattices with feature sizes down to several microns.However,the mechanical properties of as-printed polymers were not systemically studied at the relevant length scales,especially when the feature sizes step into micron/sub-micron level,limiting its reliable performance prediction in micro/nanolattice and other metamaterial applications.In this work,we demonstrate that PμSL-printed microfibers could become stronger and significantly more ductile with reduced size ranging from 20μm to 60μm,showing an obvious size-dependent mechanical behavior,in which the size decreases to 20μm with a fracture strain up to~100%and fracture strength up to~100 MPa.Such size effect enables the tailoring of the material strength and stiffness of PμSL-printed microlattices over a broad range,allowing to fabricate the microlattice metamaterials with desired/tunable mechanical properties for various structural and functional applications.

Additively manufactured heterogeneously porous metallic bone with biostructural functions and bone-like mechanical properties

A compatible artificialbone impla nt requires large pores for enhanced nutrients transports,small pores to allow cell seeding and bone-like mechanical properties to avoid stress shielding.Herein,we report novel improved gyroid lattices with millimetre-scaled gyroid wall spacings and micrometre-scaled additional pores on the walls.Designs are successfully fabricated by electron beam melting using Ti-6 Al-4 V to high part qualities while exhibiting bone-like mechanical properties with a range of Young's modulus of 8-15 GPa and strength of 150-250 MPa.The improved design also eliminates brittle failure by allowing the structure to deform more stably.