Diffusion Soldering

Abstract

Diffusion soldering is a hybrid of diffusion bonding and soldering. The principle of the process is to run a minute volume of solder into a joint between components that are pressed together and to solidify the solder by conversion to high melting point phases through isothermal reaction with the substrates. Thereafter the joint will not remelt unless heated to the temperature at which the high melting point phases melt. Tin can be used to make diffusion soldered joints between components of pure gold. The objctive of the present study was to evaluate tin as a diffusion solder for joining items of 18 carat golds, representative of alloys widely used in the fabrication of jewellery. The permissible range of the process parameters have been identified and a process specification has been developed. Joints can be made by heating to 450°C, which is substantially lower than the temperature needed for brazing of jewellery using conventional carat filler alloys. The resulting joints are colour matched and have mechanical properties that are likely to be adequate for jewellery applications. Diffusion soldering with tin has also been applied successfully to join 22 carat jewellery and the new jewellery alloy of 990 gold.