Impact of oxygen content on debinding of binder jetted 17-4 PH stainless steel: Part I - Debinding

Artikel i vetenskaplig tidskrift, 2024

Binder jetting (BJT) utilises a sacrificial binder to shape green parts in a metal powder bed. The binder must be removed during debinding at elevated temperatures without contaminating the powder material. Efficient binder removal often requires oxygen in the atmosphere to aid the decomposition of the binder, but oxygen causes oxidation of the metal powders and hence negatively impacts the final material properties. Therefore, the use of tailored oxygen contents in the atmosphere during a standard debinding cycle performed at 300 degrees C for 2 h was investigated for BJT printed 17-4 PH stainless steel. The change in bulk chemistry (carbon, oxygen, nitrogen, and hydrogen) from green parts to brown parts was thoroughly analysed and compared to the virgin powder subjected to the same conditions as used for debinding. While inert argon was beneficial for protecting the powder from oxidation, the removal of only similar to 34% of binder was insufficient, resulting in 0.47 wt.% of residual carbon in the brown part. Debinding in atmospheres containing 3 vol.% O2 to 20 vol.% O2 led to almost complete binder removal, but also caused significant oxygen pickup by the powder between 1734 ppm and 1820 ppm. Furthermore, the brittleness of the brown parts increased, leading to undesirable powder losses during handling. The best debinding was obtained in Ar + 1 vol.% O2, which allowed the best combination of binder removal of similar to 74% and lower oxygen pickup by the powder of 1617 ppm, together with sufficient brown part strength for handling.