Multiscale microstructural regulation and enhanced tensile and tribological performance of CNTs-reinforced IN718 fabricated by laser powder bed fusion

CNTs-reinforced IN718 composites were fabricated by laser powder bed fusion (LPBF) to clarify how CNT addition affects the microstructural evolution and service-related properties of the alloy. Compared with monolithic IN718, CNTs-IN718 exhibited clear grain refinement, an increased fraction of low-angle grain boundaries, and elevated local misorientation, indicating enhanced subgrain subdivision and a more defect-rich microstructure. Raman and TEM/EDS analyses further showed that part of the CNT-derived carbon framework was retained after LPBF, while carbon-containing nanoscale heterogeneities associated with Nb/Mo enrichment formed in the matrix. These multiscale structural changes led to a significant increase in hardness from 8.21 ± 0.02 GPa to 10.20 ± 0.02 GPa and in the H 3 /E 2 value from 0.00773 to 0.01972, indicating enhanced resistance to local plastic deformation. Correspondingly, the ultimate tensile strength increased from approximately 1.0 GPa to about 1.58 GPa, although accompanied by a moderate reduction in tensile ductility. In addition, CNTs-IN718 exhibited substantially improved tribological performance under dry sliding, with the wear volume and wear rate decreasing by about 54.3% and 53.4%, respectively. The improved mechanical and tribological properties are attributed primarily to multiscale microstructural regulation, including grain refinement, enhanced substructure evolution, local solute redistribution, and CNT-assisted interfacial constraint effects.