Powder-level carbide modification controls HIP grain growth and enhances fatigue in reused additively manufactured superalloy

Inconel 718 dominates laser powder bed fusion (PBF-LB/M) builds as the benchmark Ni superalloy for its γ′/γ″ hardenability, weldability, and qualification pedigree, yet its fatigue resistance remains limited by porosity, tensile residual stresses, and microstructural heterogeneity. Hot isostatic pressing (HIP) reduces porosity but induces grain growth and twinning, which degrade fatigue performance. 

Prior attempts to control grain size using micron-scale carbides often led to reduced ductility. We introduce a powder modification strategy for reused Inconel 718 feedstock by adding 0.6 wt% micron-sized niobium and titanium carbides. During PBF-LB/M, these carbides dissolve and reprecipitate as nanoscale carbide-nitrides that pin grain boundaries and refine the microstructure during heat treatment. Neutron diffraction measurements reveal a redistribution of residual stresses, linked to interactions between nano-precipitates and the alloy structure. Fatigue life improves by 150–200% in the 105–106 cycle regime, with fatigue limits up to 200 MPa higher than wrought or unmodified, additively manufactured (AM) IN718. 

This approach enables powder reuse while enhancing mechanical performance, offering a scalable route for fatigue-critical components in aerospace and energy sectors. By integrating powder chemistry and process control, this method demonstrates a sustainable strategy for upcycling aged AM powders into high-performance materials.