Binder Jetting – Impact of powder reuse and curing on powder characteristics, green parts, and sintering densification of 17-4 PH stainless steel

The influence of powder reuse on binder-jetted green parts, powder characteristics, and sintering densification was investigated for 17-4 PH stainless steel. Reusing overflow powder led to consistent printing results despite a slight humidity pickup. Powder oxidation after curing in ambient air demonstrated decreased powder packing during printing, which was connected to increased powder flowability. In comparison, curing in inert Ar preserved the powder's flowability and oxygen content. The green densities reduced from 4.71 to 4.47 g/cm 3 after 20 build jobs, while the powder's oxygen content increased by 20% due to four curing cycles in ambient air. Dilatometry of the reused samples with lower green densities revealed higher shrinkages and a change in the shrinkage anisotropy. The shrinkage of the reused samples increased mainly in the powder spreading and compaction roller axis direction as opposed to the build direction. Despite higher shrinkage, the density of the reused samples decreased compared to the virgin samples from 91.5% to 88.3% for sintering in Ar, whereas a lower reduction from 99.2% to 98.9% was detected when sintering in H 2 . Samples processed in H 2 exhibited higher sintering densification due to the formation of δ-ferrite, which was not observed for sintering in Ar. The absence of δ-ferrite was caused by a high residual carbon content, above 0.17 wt.%, due to inefficient debinding in Ar. The high carbon content also inhibited martensite formation, as indicated by a low microhardness of 159 HV0.1 compared to 315 HV0.1 for sintering in H 2 .