Spatial control of microstructure, phase transformation and actuation in NiTi lattice structures via local modulation of LPBF processing conditions

One of the captivating properties in shape memory alloys (SMAs) is their unique actuation capabilities, which is not a common property in metallic materials. The recent development of additive manufacturing technologies, like laser-powder bed fusion (LPBF), has enabled precise control of the local processing conditions enabling unprecedented freedom in both, microstructural and geometrical design of materials. However, the integration of these two degrees of freedom to spatially tailor functional behavior in SMAs remains largely unexplored. In this work, we have synergistically combined geometrical design and spatial modulation of LPBF processing parameters to realize NiTi cellular structures with spatially tunable actuation behavior. A foundational body-centered cubic (BCC) lattice geometry is locally modified through controlled variation of LPBF parameters, generating regions with distinct microstructures and transformation characteristics. This spatial differentiation enables selective activation of specific regions within the lattice during phase transformation. A near equiatomic NiTi alloy is used as the base material. Microstructural analysis and thermomechanical testing are conducted to establish the processing–microstructure–property relationships governing actuation performance. The resulting structures exhibit actuation strains ranging from 6% to 10%, depending on the spatial processing pattern, demonstrating enhanced functional tunability compared to previously reported homogeneous architectures. The presented approach establishes a foundation for process-encoded functional design in metallic cellular materials and provides a pathway toward advanced adaptive structures with region-specific actuation behavior. • The modification of SMA functional behaviour by laser powder bed fusion is studied. • Approach integrates modulation of LPBF for microstructural and structural design. • Microstructural changes identified leads to local changes in the phase transformation. • This enables a new generation of shape memory cellular structures with tailored properties. • The achieved actuation strains vary from 6%–10%, depending on the configuration.