Precious metal based bulk glass-forming liquids : development, thermodynamics, kinetics and structure

Abstract

Bulk glass-forming alloy compositions are found in various noble-metal based systems. Their superior properties and their high noble metal content predestinate these alloy classes for the application as jewelry alloys. This work is separated into two parts and focuses on the gold- and platinum-based bulk glass-forming liquids. In the case of the 18 karat white gold bulk glass-forming alloy composition Au49- Ag5.5Pd2.3Cu26.9Si16.3, a fast color change is observed which is attributed to a corrosion process when worn on human skin. A strategy to modify the alloy composition was developed and evaluated that on the one hand allows the improvement of the corrosion resistance and on the other hand maintains the ability of the liquid to form a bulk metallic glass. The second part of this work comprises the evaluation of the thermophysical properties of platinum-phosphorous-based glass-forming liquids. The thermophysical properties are used in combination with high- and lowtemperature crystallization experiments to determine the origin of the high glassforming ability. Moreover, the observed differences within the platinum-phosphorous class as well as those to the compositionally related palladium-phosphorous alloys are investigated in in-situ synchrotron X-ray scattering experiments. The results suggest that the temperature dependence of the atomic dynamics in platinum-phosphorous- based liquids is reflected by structural ordering processes on certain length scales. The differences in the representative structural units and their connection scheme between platinum-phosphorous- and palladium-phosphorous-based liquids might be responsible for the different sensitivity to annealing induced embrittlement which was already reported in literature.