Abstract
In order to improve the hardness of pure gold, alloying with small amounts of germanium (Ge) is of great interest. However, the resulting embrittlement of the new alloy is undesirable for use in jewelry applications. Thus, it is necessary to elucidate the cause of this behavior in this microalloy in order to avoid it in future cases. The Au-Ge alloy was characterized using a combination of inductively coupled plasma mass spectrometry (ICP-MS) to investigate the nominal chemistry, Vickers microhardness to determine the alloy’s hardness in comparison to pure Au, X-ray diffraction (XRD) to find the phases/structures, along with light optical microscopy (LOM) and scanning electron microscopy (SEM) to explore the alloy’s surface features including grain size, and phase distributions. A heating microscope and differential thermal analyzer (DTA) were also used in order to determine the phase transformation behavior. Trace amount of Ge was found to render Au grains refined to the size of 10 to 160 μm. The corresponding microhardness was remarkably improved from 31 to 56 HV. The Au-Ge microalloy was found to exhibit Ge enrichment along the grain boundaries, resulting in an interdendritic, eutectic that forms throughout the microstructure. This phase distribution is likely the cause of the brittle mechanical behavior of the Au-Ge alloy.
Highlights
Gold has been utilized in cultural, decorative, and financial applications since ancient times
Various deformation treatments were applied to the samples by cold working in a rolling mill
It was found that the Au-Ge microalloy displayed embrittlement
Summary
Gold has been utilized in cultural, decorative, and financial applications since ancient times. Pure gold is too soft, limiting its application in the manufacture of jewelry because it is deformed, scratches and loses its luster This is in addition to its high cost. This maintains the needs and expectations of having high-purity Au products, especially in East Asian gold markets Both kinds of alloys can be called gold-based microalloys, according to gold jewelry industry customs. It is reported the strength of gold has been greatly improved by adding trace elements [8]. With regard to the mechanical properties of the Au-Ge alloy, the literature asserts that brittleness is observed after the addition of Ge to pure gold to form the Au-Ge eutectic [13].
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