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This study explores cardiovascular stents fabricated using laser powder bedfusion (LPBF); an emerging method to offer patient-specific customisable parts.Here, the shape memory alloy NiTi, in a near equiatomic composition, wasinvestigated to deconvolve the material response from macroscopic componenteffects. Specifically, stress-geometry interactions were revealed, in-situ, fora minaturised cardiovascular stent subjected to an externally appliedcylindrical stress whilst acquiring synchrotron X-ray imaging and diffractiondata. The approach enabled the collection of spatially resolved micromechanicaldeformation data; the formation of stress-induced martensite and R-phase wasevident, occurring in locations near junctions between stent ligaments wherestress concentrations exist. In the as-fabricated condition, hardness maps wereobtained through nanoindentation, demonstrating that the localised deformationand deformation patterning is further controlled by porosity andmicrostructural heterogeneity. Electron backscatter diffraction (EBSD)supported these observations, showing a finer grain structure near stentjunctions with higher associated lattice curvature. These features, combinedwith stress concentrations when loaded will initiate localised phasetransformations. If the stent was subjected to repeated loading, representingin-vivo conditions, these regions would be susceptible to cyclic damage throughtransformation memory loss, leading to premature component failure. This studyhighlights the challenges that must be addressed for the post-processingtreatment of LABF-processed stents for healthcare-related applications.

Microscale stress-geometry interactions in an additively manufactured  NiTi cardiovascular stent: A synchrotron dual imaging tomography and  diffraction study