Improving fatigue resistance of reused AM Inconel 718 using carbide additives and HIP

Inconel 718 is widely used in industrial additive manufacturing (AM) due to its favorable combination of mechanical properties and printability. However, its fatigue life is limited by residual stresses, porosity, and microstructural defects inherent to laser powder bed fusion (LPBF). Although hot isostatic pressing (HIP) reduces porosity and microstructural variability, it may also lead to grain coarsening and increased twinning. To address these issues, we incorporate 0.6 wt.% micron-scale niobium carbide and titanium carbide into reused Inconel 718 feedstock powder. These carbides dissolve during LPBF and promote the formation of fine, nano-scale carbide-nitride precipitates during subsequent heat treatment, stabilizing the microstructure against abnormal grain growth. Neutron diffraction data indicate that these nano-precipitates help redistribute residual stresses more favorably. Fatigue testing shows a 150–200% improvement in fatigue life over conventional LPBF Inconel 718. The fatigue limit also exceeds that of wrought and aged counterparts by about 200 MPa in the 104–106 cycle range. These improvements are notable, as AM alloys generally perform poorly in low to mid-cycle fatigue due to their intrinsic defects. The proposed approach of feedstock modification combined with optimized heat treatment enables the development of AM nickel-based alloys suited for fatigue-critical applications, while also supporting powder reuse and enabling powder upcycling by enhancing the performance of reused feedstock beyond typical expectations.