Interface diffusion and sintering kinetics in fused filament fabricated 316L stainless steel under varying sintering times

Metal FFF (fused filament fabrication) offers a cost-effective powder-bed additive manufacturing alternative, though properties depend strongly on de-binding and sintering. In this study, 316 L stainless steel filaments containing metal powder and polymer binder were printed into cubes, de-bound, and sintered at 1300 °C for varying holding times of 1 h, 2 h, and 3 h. The focus was on sintering kinetics and interface diffusion to evaluate their effect on porosity, particle bonding, and mechanical properties. Results showed that with increasing sintering time, interconnected pores decreased, spherical pores became dominant, and grain boundary migration improved particle bonding. Porosity was reduced by nearly 50%, hardness increased from 114 to 249 HV, and density improved by more than 26.04%. Electron Backscatter Diffraction (EBSD) maps revealed that shorter sintering times retained strain localization at particle boundaries, while extended sintering promoted grain coalescence, development of high-angle boundaries, and crystallographic texture. Kernel Average Misorientation (KAM) and Geometrically Necessary Dislocation (GND) analysis further confirmed reduced strain concentration at particle interfaces with longer sintering. These findings demonstrate that control of sintering time governs the transition from incomplete bonding to advanced diffusion and densification, directly linking porosity and particle interfaces with mechanical performance in Fused Filament Fabricated 316 L stainless steel.