Investigation of texture evolution and multi-mechanism strengthening in NiTi alloy produced via selective laser melting

Abstract

The mechanical performance of NiTi alloys is strongly governed by microstructural features such as densification, grain morphology, and dislocation density. However, quantitative insights into how processing parameters systematically control grain size, high-angle grain boundary (HAGB) fraction, texture characteristics, and kernel average misorientation (KAM) to achieve targeted property tuning remain limited. This study integrates experimental analysis, thermo-fluid coupling simulations, and theoretical modeling to systematically investigate the effects of laser power (100–140 W) and scanning speed (900–1100 mm/s) on the densification behavior and microstructural evolution of NiTi alloys fabricated by selective laser melting (SLM). The simulations reveal the evolution of Marangoni convection within the melt pool under varying energy densities, while metallographic analysis quantifies the correlation between porosity and processing parameters. The optimal process parameters (130 W, 1000 mm/s) yielded a tensile strength of 549 MPa, elongation of 6.39 %, elastic modulus of 21.04 GPa, and microhardness of 316–321 HV. EBSD analysis showed HAGB fractions of 41.7 % (X–Z) and 41.4 % (X–Y), with average grain sizes of 19.03 μm and 27.44 μm. TEM revealed abundant linear dislocations and uniformly dispersed NiTi₂ precipitates. These results demonstrate that the combination of high densification, strong texture, and multiple strengthening mechanisms enables a favorable balance of strength and ductility, thereby providing both theoretical guidance and practical insights for optimizing SLM-processed NiTi alloys.