Shape memory alloys (SMAs) are a class of materials with unique thermomechanical properties arising from the austenite–martensite transformation. The change of these properties has historically relied on microstructural changes through alloy design and thermomechanical heat treatments. In this work, laser powder bed fusion (LPBF) has been used to locally modulate the energy input during manufacturing to generate spatially heterogeneous microstructures within a single composition. Microscopy analysis confirms the presence of heterogeneous microstructures, including Ti 2 Ni precipitates in regions processed with higher laser powers. The patterned materials are thermally cycled to determine their transformation temperatures. The transformation temperatures show a strong dependence on pattern geometry. This dependence is discussed in terms of interface density and geometry, and their potential influence on local thermal history and internal stress fields. The patterned materials are further trained to evaluate their two-way shape memory effect. The recoverable strain exhibits a clear dependence on pattern configuration. This behaviour is interpreted in terms of microstructural heterogeneity and transformation compatibility across interfaces. The unrecoverable plastic strains are associated with the formation of columnar grain structures during the LPBF process. Overall, this work extends previous studies on graded LPBF NiTi by highlighting the role of interface geometry and topology within a single composition system in governing transformation behaviour, providing a pathway toward the design of SMA metamaterials with spatially tailored properties. • Spatial LPBF energy modulation enables graded NiTi SMA metamaterials. • SMA transformation behaviour can be modulated by the pattern geometry. • Ti 2 Ni precipitation controlled by local VED variation. • Vertical interfaces govern the local stress and phase compatibility. • Combined experimental–computational study reveals interface effects.
Garrido et al. (Fri,) studied this question.