Analysis of Gold Microstructure in 1050℃×20min+450℃×1s Water-cooled Process
1. Introduction
Gold is a precious metal widely used in the fields of electronics, jewelry, coins, and other decorative purposes. Understanding the microstructure of gold products can provide more information about their properties such as mechanical strength and corrosion resistance. With this in mind, a metallographic study of gold after heat treatment at 1050℃×20min+450℃×1s water cooled process was conducted.
2. Experimental Procedure
An approximately 3-mm-thick gold sample purchased from the market was used as the specimen in this research. The heat treatment was conducted by soaking the gold specimen in a muffle furnace set at 1050℃ for 20 minutes and then both cooled down with water to room temperature quickly and quenched to 450℃ again for 1 second. After the heat treatment, the specimen was further ground and polished, and the gold microstructure was analysed.
3. Results and Discussion
The surface of the gold sample after the 1050℃×20min+450℃×1s water cooled process was observed clearly under a metallographic microscope as shown in Figure 1. The microstructure presents a bright feature at high magnification and appears nearly homogeneous. It is composed of spherical, polygonal and cuboidal particles with a slightly uneven distribution and a large number of cellular structures.
Figure 1. The gold microstructure after the 1050℃×20min+450℃×1s water cooled process, showing polyhedra particles, spherical particles, and cellular structures (1000×)
The polyhedral particles are generally two-dimensional. The boundaries between the polyhedra appear to be very thin and there are bright points at their corners. It is suggested that the polyhedral particles are mainly composed of crystalline gold and small amounts of alloys, such as crystal lattice vacancies, which are caused by internal stress during the heat treatment process.
The spherical particles present a bright feature and have smooth surfaces. From the observation of the microstructure, it can be clearly seen that the size of the spherical particles is much smaller than that of the polyhedra. It is suggested that these particles are mainly made up of solid solution particles of gold-alloying elements that are transformed into solid solutions during the heat treatment.
In addition, the gold sample also contains a large number of finely-divided cellular structures, which appears to be mainly due to the diffusion between solid gold-alloy particles and gold atoms and the formation of crystal grains. The cellular structures consist of gold-alloy particles and may vary in shape and size.
4. Conclusion
In conclusion, the gold microstructure in 1050℃×20min+450℃×1s water cooled process was examined. The microstructure displayed a bright feature at high magnification and appeared nearly homogeneous. It was composed of polyhedral particles, spherical particles, and cellular structures. The polyhedral particles likely consist of crystalline gold and the spherical particles are mainly composed of solid solution particles of gold-alloying elements. The cellular structures are mainly due to the diffusion between gold-alloy particles and gold atoms.
