The present paper describes the results of a collaborative research project on the selective laser melting of 18-karat gold alloys. Three main objectives were pursued during the project: (1) to analyze the effect of the process parameters, (2) to investigate the role of powder treatments and alloy composition and (3) to identify design rules for additively manufactured jewelry items. Laser power, layer thickness, scan rate and overlap of the scans were optimized in order to reduce the porosity of the parts built in 18K yellow-gold alloy. The production of defect-free parts in gold, silver or copper alloys is challenging due to their high reflectivity and thermal conductivity. It will be shown that using a partial oxide layer of several tens of nm thickness on the surface of the powder significantly reduced porosity compared to using untreated powder. The ability of alloys that contained additions of 0.3-0.7% Fe, Ti or Ge to reduce reflectivity and thermal conductivity was also studied.

Author: Dr. Ulrich E. Klotz