NiTi porous structure with 3D interconnected microchannels using steel wire spaceholders

NiTi porous structures with fully 3D interconnected microchannels were created by a powder-metallurgy method using steel wires as spaceholders. Prealloyed NiTi powders were near-fully densified by hot pressing within a high carbon steel wire scaffold, which was then electrochemically dissolved. This resulted in a regular 3D network of orthogonally interconnected microchannels with ellipsoidal cross-sections with 60% volume fraction. The measured elastic stiffness of 14 GPa compares well to porous and composite models, as well as finite element modeling despite varying geometry and deformation model assumptions. The structure, which is martensitic at room temperature, exhibits brittle fracture at a relatively low stress of 88 MPa due to a TiC interphase at all NiTi powder boundaries. The volume fraction, orientation, shape, and spatial distribution of the microchannels is fully controlled with this method. This makes the structure attractive for biomedical applications, specifically bone implants. The potential shape memory properties achievable through optimized processing would also make the structure effective for energy absorption or actuators.