Microstructural Insights to NiTiNb Shape Memory Alloys Made via Extrusion AM

Additively manufactured NiTi with Nb as a sintering aid has been shown to demonstrate shape memory properties, opening opportunities for advanced multifunctional design. However, the microscale mechanical behavior of these alloys remains an open area of exploration, particularly regarding high strain-rate deformation and the impact of sintering alloys on local mechanical properties. Through nanoindentation mapping, we investigate the hardness of local microstructures in 3D printed NiTi with varying concentrations of Nb over strain rates across several orders of magnitude. Alloys are produced via filament extrusion 3D printing and undergo a post-printing sintering process to reduce porosity. The microstructural features are characterized through a suite of experiments including SEM, EDX, XRD, Rutherford backscattering spectroscopy (RBD), and elastic recoil detection analysis (ERDA). By illuminating the contributions of specific features like Nb-rich regions, oxide inclusions, and interfaces, we highlight the role of specific microstructural features in localized mechanical response. We also quantify the role of small impurities and solutes unique to the printing process as compared to traditional powder sintering. These findings help provide insight for future microstructural design and reveal the relationship between the additive process and micromechanical response.