In-situ and ex-situ X-ray 3D-tomography is used to characterize the microstructure of Ni microwires, with wire diameters spanning 25–100 μm, (i) after vapor-phase deposition of Ti onto their surface and (ii) after subsequent homogenization to achieve the near-equiatomic NiTi composition desired for shape-memory or superelastic behavior. After Ti deposition at 925 °C, wires are partially homogenized, exhibiting a pure Ni core surrounded by concentric shells of Ni₃Ti, NiTi and NiTi₂ intermetallic phases. Because of the imbalanced Ni and Ti diffusive fluxes, Kirkendall porosity is formed near the center of the wire, which often merges into a single pore in cross-sections, due to spatial confinement of the wire geometry. During subsequent homogenization at 925 °C, these Kirkendall pores grow due to further Ni-Ti interdiffusion, and they coalesce into a single, hollow channel near the central axis of the wire, thus forming a NiTi microtube. In some cases, off-center pores form in addition to the central pore, but these off-center pores do not form continuous channels.

原位和异位X射线3D断层扫描用于表征Ni细线的微观结构，其线径范围为25–100μm，（i）在将Ti气相沉积到其表面后，以及（ii）随后进行均质化，以获得形状记忆或超弹性行为所需的近等原子NiTi成分。在925°C下沉积Ti后，导线被部分均化，呈现出纯Ni核，被Ni ₃ Ti，NiTi和NiTi _2的同心壳包围金属间相。由于Ni和Ti扩散通量的不平衡，在金属丝中心附近形成了Kirkendall孔隙，由于金属丝几何形状的空间限制，其横截面通常合并为一个孔。在随后的925°C均质化过程中，由于进一步的Ni-Ti相互扩散，这些Kirkendall孔生长，并且它们聚集成线中心轴附近的单个中空通道，从而形成NiTi微管。在某些情况下，除了中心孔之外，还会形成偏心孔，但是这些偏心孔不会形成连续的通道。