Binder‐Governed Densification in DIW 316L: Comparison of Nanocellulose and Carboxymethyl Cellulose Binders and the Role of Sintering Atmosphere

Direct ink writing (DIW) offers a low cost, water‐based route to metal additive manufacturing; however, drying induced distortion and entrapped air often generate green body defects that persist as residual porosity after sintering. Here, nanocrystalline cellulose (NCC) and carboxymethyl cellulose (CMC) binders are compared for DIW of 316L stainless steel to simplify processing and improve densification. Rheological measurements show that NCC‐based inks exhibit higher yield stress 100 Pa and faster structural recovery 94% than CMC‐based inks (20 Pa, 88%), resulting in improved filament stability and shape retention. NCC inks can be printed and dried at room temperature, whereas CMC inks require a heated substrate to reduce deformation. Cuboid specimens were sintered at 1350 °C under argon or vacuum. Vacuum sintering improved densification for both binder systems. NCC‐based samples sintered under vacuum achieved the highest Archimedes relative density of 97.1% ± 2.3% TD with an ImageJ pore area fraction of ∼2.2%, reduced surface oxidation and hardness (∼133 HV 5 ) with low scatter, while CMC inks produced 3.5% porosity under vacuum and 9.6% under argon, confirming that atmosphere affects densification across both binder chemistries. These results demonstrate that binder selection governs rheology, drying behavior, and defect formation in DIW of metals.