Sintering behaviour of 3D-printed 18K 5N gold alloy by binder jetting: a preliminary study

Binder jetting is a versatile additive manufacturing technique suitable to produce alloys that are difficult to obtain by powder bed fusion techniques, such as precious metals, due to their high reflectivity and thermal conductivity. In this study, a 18K 5N gold alloy powder was employed in the printing process. Different heat treatments and densification processes were employed to achieve final-stage sintering and remove residual porosity, whilst controlling the evolution of copper oxides by reduction with hydrogen and graphite. Powder, green and sintered samples were characterised at the microstructural level by X-ray diffraction, microscopy and energy dispersive X-ray spectroscopy to assess phase transitions and secondary-phase formation. Oxide-free components with a final relative density above 90% were achieved by densification at 830 °C combined with carbon- and CO-induced reduction of tenorite and cuprite. The optimal manufacturing route was chosen to produce a bezel, as a case study for the adoption of this technique in the jewellery industry.