Influence of laser powder bed fusion parameters on deformation behavior and stress-induced martensitic transformation in NiTi alloys at constant volumetric energy density level

This study systematically investigated the microstructure evolution, crystallographic texture development, and stress-induced martensitic transformation (SIMT) behavior of NiTi shape memory alloys fabricated by Laser Powder Bed Fusion (LPBF). Two distinct processing regimes were examined using in-situ synchrotron-based high-energy X-ray diffraction (HE-XRD) and electron backscatter diffraction: (i) low laser power with low scanning speed (Sample I) and (ii) relatively high laser power with high scanning speed (Sample II). Both regimes were designed to achieve the same volumetric energy density level. Sample I exhibited more randomly oriented and coarser grains, along with higher porosity, while Sample II developed a strong ⟨001⟩ fiber texture along the build direction in the austenitic phase, with a reduced defect density being observed. In-situ HE-XRD tensile experiments with loading direction (LD) parallel to the horizontal direction (parallel to building direction) demonstrate greater ductility, a flatter SIMT plateau, and a higher martensitic transformation rate for Sample I. Significant grain-to-grain interaction among oriented martensitic grains arises with deformation in both LPBF samples as evidenced by the observed negative lattice strain of [111]//LD martensitic grains. These findings provide critical guidelines for optimizing LPBF parameters to tailor the functional properties of NiTi shape memory alloys. © 2025 Elsevier B.V.