Enhanced mechanical properties of selective laser melted Y-doped Hastelloy X alloy via core–shell precipitation and grain refinement

Hastelloy X (HX) is widely used in high-temperature aerospace components because of its excellent mechanical strength, oxidation resistance, and corrosion resistance. However, selective laser melting (SLM) of HX alloys is still limited by coarse columnar grains, elemental segregation, thermal cracking, and an insufficient strength–ductility balance. In this study, HX alloys with different Y 2 O 3 additions (0–1 wt.%) were fabricated by SLM, and the effects of Y 2 O 3 nanoparticles on microstructural evolution and mechanical properties were systematically investigated. The results show that appropriate Y 2 O 3 addition significantly refined the microstructure of SLM-fabricated HX alloys. At 0.5 wt.% Y 2 O 3 , the average grain size decreased from 27.72 μm to 18.58 μm, while the fraction of low-angle grain boundaries increased from 41.8% to 47.5%, indicating enhanced dislocation accumulation and substructure formation. In addition, a characteristic Y 2 O 3 @M 23 C 6 core–shell structure formed, in which Y 2 O 3 particles promoted the precipitation of Cr- and Mo-rich carbides, generating synergistic oxide dispersion and interfacial-strengthening effects. Mechanical testing demonstrated that the 0.5 wt.% Y 2 O 3 sample achieved the optimal strength–ductility balance. The room temperature tensile strength increased from 754.13 to 881.63 MPa, and the tensile strength at 750 °C increased from 461.33 to 532.50 MPa, while elongation improved from 10.56% to 26.21%. These enhancements were mainly attributed to grain refinement, Orowan strengthening, dislocation pinning, and interfacial strengthening. Excessive Y 2 O 3 addition caused particle agglomeration and stress concentration, resulting in performance degradation. Overall, nano-Y 2 O 3 addition provides an effective strategy for optimizing the microstructure and mechanical properties of SLM-fabricated HX alloys.