Alloying and strengthening of gold via rare earth metal additions

Abstract

A sketch map of simplified phase diagrams for Au-RE systems has been plotted and the interactions and the alloying behaviour between gold and the rare earth (RE) metals are summarized in this paper. The solid solubilities of the rare earth metals in gold increase as their atomic number increases. The solid solubilities and alloying behaviour of yttrium and scandium are dose to and similar to those of dysprosium and lutetium, respectively. The factors influencing the solid solubility are discussed. Hume-Rothery and Darken-Gurry proposed that the relationship between atomic size and electronegativity was a criterion for solid solubility. This can be revised for the alloying behaviour between gold and RE metals. The maximum solubility of RE metals in gold is greater than 1.0 at% RE when the difference in atomic size is less than 25% and that of the electronegativity is less than 0.7 units. The.relationship between the way in which the intermediate phases that exist in the various Au-RE systems areformed and their respective crystal structures .are also summarized. The changes in transformation temperatures of eutectic reactions and the various intermediate phases, expressed as ratios with the melting points of gold or the RE metals, have been studied in relation to the atomic sizes and atomic numbers of the RE metals. These temperature ratios decrease as the atomic numbers of the RE metals increase although those for cerium and ytterbium have anomalously high values. The trends in the distribution and strengthening effect of RE metals present as trace or dilute solute in gold are discussed.

A survey of gold intermetallic chemistry

“…It has been shown that such regularities may be useful in predicting and designing alloying behaviour, as shown in several groups of rare earth alloys (see, for instance, refs (17,18,19). Analogous comments have been presented in a recent paper by Ning (20) in which strenghtening of gold via rare earth metal additions has also been described. Fig.…”

Thermodynamic calculations of the Au–Sc and Fe–Sc systems

“…Recently, Wang et al [3] have discussed the plasticity of the scandium-based nanoglass. Moreover, Scandium addition into gold alloy can significantly strengthen alloy and raise the recrystallization temperature [4]. The phase equilibria and thermodynamic properties in the Au-Sc and Fe-Sc systems are of great importance for the designing of related new materials.…”

Hardening of Low-Alloyed Gold

“…This holds especially for 24ct jewellery alloys with a minimum of 99-99.5% Au depending on individual national legislation. Former studies (6,7,8) that are summarised in another source (1), have focused on microalloying additions of (light) metals with a promising potential for solid solution hardening due to a large difference in atomic size and weight to pure gold. Other studies focused on microalloying with rare-earth, refractory or light metals/elements.…”