Microstructure‐Pore Defect‐Property Relationship of NiTi Alloy Fabricated by Laser Powder Bed Fusion: Experimental and Numerical Analysis

This study aims to reveal the interaction between the microstructure, keyhole‐induced pore defects, and mechanical properties of NiTi alloy fabricated by the laser powder bed fusion (LPBF) method. The results indicate that as the laser scanning speed increases, the grain size of the NiTi alloy gradually decreases, and the nanoindentation hardness and modulus gradually increase. At higher scanning speeds, the crystallographic orientation progressively deviates from <001>, resulting in diminished superelasticity and significant fluctuations in the micromechanical and damping properties of materials near defect areas. At lower scanning speeds, the keyhole depression created by the recoil pressure in the molten pool area further collapses, resulting in more pore defects. Defects change the direction of the flow field and the distribution of the temperature field in the microarea during their formation and movement, altering the temperature gradient and solidification rate of the microstructure near the defect. Differential grain growth occurs around the defect, resulting in anisotropy of micromechanical properties. The obtained results provide a comprehensive analysis of the intrinsic correlation between the defect characteristics and material properties of LPBF NiTi alloys under different process parameters.