ZrB₂-induced microstructural evolution for strength–ductility synergy in LPBF-fabricated GH3536 composites

In this study, a GH3536 nickel-based superalloy was modified by the addition of 1 wt% ZrB₂ nanoparticles and fabricated via laser powder bed fusion (LPBF). CALPHAD thermodynamic simulations, in conjunction with experimental characterization, indicate that ZrB₂ may undergo partial decomposition or interfacial reactions within the high-temperature molten pool. The released Zr and B atoms exhibit distinct solidification behaviors due to differences in their chemical activities. Specifically, B atoms preferentially combine with Mo and Cr to form M₃B₂-type borides, whereas Zr atoms, owing to their low partition coefficient, segregate during the terminal stages of solidification to form Ni₅Zr intermetallic compounds. These two types of precipitates are distributed in a chain-like morphology along cellular substructure boundaries. Benefiting from the high growth restriction factor of Zr, the solute-induced growth restriction effect effectively suppresses the epitaxial growth of columnar grains, resulting in a significant grain refinement from 26.79 μm to 4.49 μm, corresponding to a reduction of 83%. In terms of mechanical performance, the modified alloy exhibits a yield strength of 864.5 MPa at room temperature and 425.3 MPa at 800 °C, along with a machine-displacement-derived strain at fracture of 18.7% at 800 °C. Compared with the base alloy, the room-temperature yield strength, high-temperature yield strength, and machine-displacement-derived strain at fracture increased by 64%, 37%, and 202%, respectively, demonstrating an excellent balance between high-temperature strength and deformation capacity. Further analysis indicates that the enhancement in room-temperature strength arises from the combined effects of grain-boundary strengthening and Orowan strengthening, while the improved high-temperature deformation capacity is associated with grain refinement and the disruption of continuous columnar grain boundaries, which promote more homogeneous deformation, mitigate GBS-induced damage accumulation, and delay intergranular cracking. This work provides valuable insights into the role of ZrB₂ addition in tailoring the microstructure and mechanical properties of LPBF-fabricated GH3536 alloys.