Decoupling the effects of pore and microstructure on the high-temperature performance of the laser powder bed fusion-fabricated 17–4 PH steel

Effective pore elimination is essential for enhancing the high-temperature performance of additively manufactured components. However, different elimination strategies often induce microstructural changes, leading to distinct mechanical behaviors. In current research, the effects of pores and microstructure are interdependent and difficult to decouple experimentally. This study combines molecular dynamics (MD) simulations and experiments to isolate their individual impacts. MD models with varying pore sizes were used to assess pore effects, while nearly dense samples were used experimentally to evaluate microstructural contributions. MD results reveal that pores serve as failure initiation sites, significantly reducing tensile strength. Larger pores further degrade strength and shift deformation mechanisms from dislocation glide to a combination of glide and deformation twinning. Experimentally, achieving a nearly pore-free BCC structure in as-built PBF-LB 17–4PH is challenging. Process-optimized samples contained 5.2 % retained austenite and exhibited a refined grain size of 11.1 μm. Compared to porous reference samples, their ultimate tensile strength (UTS) increased by 1.8–8.9 %, and elongation improved by 16.1–78.1 %. HIP-treated samples achieved a dense, uniform BCC structure and showed 11.3–30 % UTS improvement, though their elongation dropped by 26.4 % and 16.6 % at 450 °C and 500 °C, respectively, while maintaining good toughness. The microstructural features include Cu-rich precipitation, phase composition, and grain size, which play a crucial role in strengthening and fracture. This study successfully decouples the roles of pore and microstructure in high-temperature mechanical behavior, clarifies their individual mechanisms, and reveals trade-offs between strength and ductility associated with different pore elimination strategies.