The impact of oxidation during curing of binder jetted 17-4 PH stainless steel on powder properties and powder surface chemistry

Binder jetting is an additive manufacturing process that selectively joins powder particles with a liquid binder to create complex 3D objects. Achieving final material properties requires subsequent curing, debinding, and sintering. This study investigates the degradation mechanisms of 17-4 PH stainless steel powder during multiple reuse and curing cycles in the BJT process. X-ray photoelectron spectroscopy (XPS) is employed to analyze changes in the surface chemistry of the powders. XPS results demonstrate the increase of the oxide layer thickness from ~4.3 nm to ~7.1 nm with powder conditioning. After the first curing process, the oxide layer thickness increased to ~9.5 nm, but following curing cycles showcased minimal changes. These findings agree with bulk oxygen measurements, where the oxygen content increased from ~730 ppm of the unconditioned sample to ~1300 ppm after conditioning. After the first curing, the oxygen content rose to ~1500 ppm, whereas the subsequent curing did not alter the oxygen content much. The uptake of oxygen results in elevated flowability and packing behaviour due to the passivating oxide layer on the surface of the particles. The findings provide insights into the factors affecting powder reusability and the potential impact on the final part quality in BJT.