In additive manufacturing (AM), inhomogeneous precipitates from variable thermal cycles degrade mechanical properties and fatigue life. We propose a novel large-small melt pool coupling strategy to fabricate NiTi shape memory alloy (SMA) with an architectured microstructure containing homogeneous coherent nanoprecipitates. This approach actively designs the spatiotemporal distribution of thermal cycles, where large melt pools ensure material forming while secondary low-energy lasers create smaller melt pools to enable precise in-situ heat treatment. Consequently, Ti 4 Ni 2 O x nanoprecipitates transform from an initial intergranular network into a homogeneous distribution. The resulting NiTi SMA exhibits significantly enhanced low-cycle superelastic fatigue life, outperforming all reported AMed NiTi. This superior performance stems from synergistic effects of the architectured microstructure: during loading transfer between two characteristic zones governed by strain compatibility, the homogeneous nanoprecipitation strengthening in the in-situ heat-treated zones enhances superelastic recovery and delays microcracking, while cooperative deformation in the remelted zones minimizes damage accumulation. This methodology transforms the remelting process into a precise microstructural design tool, enabling the fabrication of high-performance complex engineering components.
Cai et al. (Mon,) studied this question.