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Additive manufacturing processes such as selective laser melting and electron beam melting require small particle sizes. A widely used technique to produce suitable powders is closecoupled atomisation. To further decrease the achieved particle sizes, the annular geometry of the gas nozzle is changed to a convergent-divergent (CD) profile. This novel configuration is capable of operating stably at low pressures of 0.8 MPa and above. Beyond that, the unwanted effects of lick-back are avoided. Different nozzles with conventional and convergent-divergent annular geometry have been designed based on fluid-flow calculations. The aspiration pressure was measured to determine stable process windows. Powders from a CuSn alloy were produced using cold and hot gas atomisation to show the influence on the process stability, particle size and morphology. High-speed recordings are used to investigate the process conditions of the different nozzle configurations.

The attractive color of blue and especially purple gold alloys has always intrigued jewelry designers and producers. The reality of using these colors for jewelry has been very limited, however, mainly due to the inherent brittleness and poor corrosion resistance of this special class of gold alloys. The paper reports on some improvements in crack resistance that are obtained by particular additions to 14k blue-and 18k purple-gold colored alloys. Opportunities to incorporate such colors in jewelry design with these modified, colored-gold alloys using investment casting (as well as the still existing limitations) are discussed. Special attention is given to bi-metal casting technologies that can be used to manufacture multi-colored jewelry. A protective, transparent and wear-resistant coating finally needs to be applied to minimize corrosion and improve long-term stability of the colorful pieces.

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