Effect of Preprocessing Temperature On the Recycling of Waste Direct Metal Laser Sintering Powder

Direct metal laser sintering (DMLS) is one of the well-known 3D printing processes for the preparation of functional prototypes. One of the limitations of DMLS is the reusability/ recyclability of the process consumables (waste metallic powder). In the past, some studies testified to the reusability of waste metallic powder of DMLS to support a circular economy. But hitherto little has been reported on investigations of recycled DMLS powder collected in mixed form (comprising more than one metallic alloy). This study highlights the investigations performed on mixed bio-compatible metallic powder (90% of 17–4 precipitate hardened stainless steel and 10% of Ti-6Al-4 V) collected (as waste) from the institute laboratory. During the pilot run, the samples were 3D printed on DMLS at different energy densities (ED) (66.66, 71.42, 90.67 J/mm³) selected based on the combination of available input parameters (i.e., laser power (LP), scanning speed (SCS), hatch distance (HD), layer thickness (LT), etc.), but all samples failed while printing. For successful 3D printing, the collected waste powder was preprocessed for thermal treatment (leading to chemical decomposition) at two different temperatures (550 °C (below recrystallization temperature) and 800 °C (above recrystallization temperature)). The preprocessed mixed powder at 550 °C was successfully 3D printed with ED 71.42 J/mm³ (attained with LP 120W, SCS 800 mm/s, HD 70 µm, LT 30 µm). The printed samples resulted in Young’s modulus (E) of 4155 MPa (in tensile) and 211 MPa (in flexural) along with a surface hardness of 335.9 HV at 50N. The in vitro studies outlined a corrosion rate of 0.000411 mm/year for a mixed powder-based functional prototype. Also, the specific wear rate was observed as 0.000036mm³/NM. The outcomes are also braced by scanning electron microscopy and energy dispersive spectroscopy (EDS) analysis.