Mechanical anisotropy of shape-memory NiTi with two-dimensional networks of micro-channels

Ni–51.4 at.% Ti (Nitinol) containing 24 and 34 vol.% orthogonally interweaving micro-channels with 350–400 μm diameters was fabricated by a powder-metallurgy method. NiTi powder preforms containing steel wire meshes arranged in parallel layers were hot-pressed into NiTi/steel composites, from which the meshes were removed electrochemically, thereby producing micro-channels with tailorable morphology, fraction, and orientation. The compressive stiffness (15–35 GPa) and strength (420–780 MPa) can be controlled by the volume fraction and orientation of the micro-channels. Stiffness values are compared against analytical foam and composite models. A combination of elasticity, superelasticity, and the shape-memory effect allows for high strain recovery (93–95% of an applied compressive strain of 5%).