Effects of Copper (Cu), Indium (In), Tin (Sn), Antimony (Sb) and Zinc (Zn) in Sterling Silver Alloys on Mechanical Properties Improvement

摘要

The jewelry industry has been searching for sterling silver with high hardness values as it is believed by the industry to have direct effect on scratch resistance as well as improved mechanical properties such as "spring" property. Even though the direct relationship between hardness and how springy the jewelry articles are could not be linked. However it is a conventional wisdom of goldsmith to observe the usual trend for alloys with higher hardness to be more elastic. Moreover it is a common and cheap test to apply to a jewelry article. Therefore it is common find jewelry manufacturers to discuss and compare hardness values. The current commercial alloys could reach 140-170 HV after careful heat treatments and/or mechanical treatments. In our research, we focused on a systematic alloy development study of ultra-hard silver alloy systems. These systems could reach high hardness values in as-cast state without subsequent post-processing treatments. The complex system comprises of silver content in the range of 80.0-92.5 wt.-% with supersaturated matrix. Twenty-two alloying element candidates and fifteen supersaturated ternary and quaternary compositions were investigated. Vickers hardness tests were performed on prototyped alloy ingots. X-ray diffraction analysis was used to measure the lattice distortion as well as to identify second or third phases in the alloys, if they existed. Metallography and electron microscopes were used to identify the microstructures. Seven developed alloy systems were presented in this paper as the investigation led to the discovery of a quaternary ductile alloy system with the hardness value of 142 HV as cast. The microstructure of the quaternary alloy was mostly single phase and these preliminary results suggested the alloy could be a good candidate for jewelry application.