Characterization of Filigree Additively Manufactured NiTi Structures Using Micro Tomography and Micromechanical Testing for Metamaterial Material Models

This study focuses on the influence of additive manufacturing process strategies on the specimen geometry, porosity, microstructure and mechanical properties as well as their impacts on the design of metamaterials. Filigree additively manufactured NiTi specimens with diameters between 180 and 350 mu m and a nominal composition of Ni50.9Ti49.1 (at %) were processed by laser powder bed fusion in a first step. Secondly, they structures were characterized by optical and electron microscopy as well as micro tomography to investigate the interrelations between the process parameters, specimen diameters and microstructure. Each specimen was finally tested in a micro tensile machine to acquire the mechanical performance. The process strategy had, besides the resulting specimen diameter, an impact on the microstructure (grain size) without negatively influencing its quality (porosity). All specimens revealed a superelastic response while the critical martensitic phase transition stress decreased with the applied vector length. As a conclusion, and since the design of programmable metamaterials relies on the accuracy of FEM simulations, precise and resource-efficient testing of filigree and complex structures remains an important part of creating a new type of metamaterials with locally adjusted material behavior.

Automated summary

This study investigates the influence of additive manufacturing process strategies on the geometry, porosity, microstructure, and mechanical properties of specimens, and their impact on the design of metamaterials. Nickel-titanium specimens with diameters ranging from 180 to 350 μm were additively manufactured using laser powder bed fusion. The specimens were characterized using various microscopy techniques to understand the relationship between process parameters, specimen diameter, and microstructure. Mechanical performance was evaluated through micro tensile testing. The study found that the process strategy affected the microstructure of the specimens without compromising quality, and all specimens exhibited a superelastic response.