Development of a platinum casting alloy for jewelry and watchmaking

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Even in the field of precious metals, platinum stands out far from the other rare elements and does inevitably experience a boom in the jewelry industry. This is due not only to the high monetary stability, but also to the excellent properties with regard to oxidation and bio compatibility. However, in addition to all the good properties of platinum, there are also some characteristics which challenge the jewelry manufacturers. Like many pure elements, platinum is very soft and therefore it is not suitable as a pure element for everyday use. The addition of alloying elements, which promote better mechanical and microstructural properties, are strictly limited since the piece of jewelry must have a minimum platinum content of 95 wt.%. In addition to the constrictions platinum is challenging due to its high melting point of 1769°C. This work presents novel compositions of platinum jewelry alloys for casting which are compared to the currently often used PtGa2.9Cu1.8 alloy. The comparison of the alloys is based on the castability and the resulting microstructure which is investigated by using scanning electron microscopy, electron backscatter diffraction analysis, energy-dispersive X-ray spectroscopy and X-ray diffractometry. Hardness measurements and tensile tests with miniature specimen reveal the mechanical properties of the alloys which are important for jewelry application.