  This study explores cardiovascular stents fabricated using laser powder bed
fusion (LPBF); an emerging method to offer patient-specific customisable parts.
Here, the shape memory alloy NiTi, in a near equiatomic composition, was
investigated to deconvolve the material response from macroscopic component
effects. Specifically, stress-geometry interactions were revealed, in-situ, for
a minaturised cardiovascular stent subjected to an externally applied
cylindrical stress whilst acquiring synchrotron X-ray imaging and diffraction
data. The approach enabled the collection of spatially resolved micromechanical
deformation data; the formation of stress-induced martensite and R-phase was
evident, occurring in locations near junctions between stent ligaments where
stress concentrations exist. In the as-fabricated condition, hardness maps were
obtained through nanoindentation, demonstrating that the localised deformation
and deformation patterning is further controlled by porosity and
microstructural heterogeneity. Electron backscatter diffraction (EBSD)
supported these observations, showing a finer grain structure near stent
junctions with higher associated lattice curvature. These features, combined
with stress concentrations when loaded will initiate localised phase
transformations. If the stent was subjected to repeated loading, representing
in-vivo conditions, these regions would be susceptible to cyclic damage through
transformation memory loss, leading to premature component failure. This study
highlights the challenges that must be addressed for the post-processing
treatment of LABF-processed stents for healthcare-related applications.
