Compression Behavior of Graded NiTi Gyroid-Structures Fabricated by Laser Powder Bed Fusion Additive Manufacturing Under Monotonic and Cyclic Loading

Both uniform and graded gyroid cellular structures (GCSs) of NiTi have been successfully fabricated by laser powder bed fusion (LPBF) additive manufacturing. NiTi GCSs were produced with gradients along two different directions, and the surface morphology and mechanical properties of different GCSs were systematically studied using micro-x-ray computed tomography, monotonic compression, and compression–compression fatigue testing. The results showed that all the LPBF NiTi structures exhibited similar nominal compressive elastic modulus (5–7 GPa) to human bones. By altering the density distribution of the novel GCSs, different deformation and fatigue properties were achieved. GCSs with graded density parallel to each layer (Y-GCSs) exhibited a similar shear compression failure behavior and slightly better fatigue behavior compared to the uniform structure. In contrast, GCSs with graded density parallel to the building direction (Z-GCSs) exhibited a layer-by-layer deformation and collapse behavior under compression, while the fatigue life was worse than the uniform structure.