Publication

Influence of thermo-mechanical processing on ordering kinetics in 18 karat red gold alloy

Marina Garcia Gonzalez
2020
EPFL thesis
Abstract

The aim of this project is to understand the correlation between alloy composition and the build-up of internal stresses in 18 carat Au-Ag-Cu alloys under thermo-mechanical loads. The copper rich end of this ternary system exhibits order-hardening of the equiatomic AuCu phase. There is very limited information in literature on the ordering transformation behavior of the copper-rich alloys under anisothermal annealing and in a pre-deformed state; and more importantly, how does the misfit strain induced by ordered nano- precipitates affect internal stresses of the material. The link between microstructural evolution and residual stresses is lacking. This project aims to quantify the coupling between the morphology of ordered precipitates and the evolution of residual stresses in pre-deformed samples, via in-situ temperature experiments with synchrotron x-ray and neutron diffraction and scattering methods. Electron microscopy will complement the microstructural investigations. This study will shed light on how thermo-mechanical loads impact internal stresses on 18 carat Au-Ag-Cu alloys subject to order-hardening of equiatomic AuCu.

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Related concepts (36)
Copper
Copper is a chemical element with the symbol Cu (from cuprum) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkish-orange color. Copper is used as a conductor of heat and electricity, as a building material, and as a constituent of various metal alloys, such as sterling silver used in jewelry, cupronickel used to make marine hardware and coins, and constantan used in strain gauges and thermocouples for temperature measurement.
Precipitation hardening
Precipitation hardening, also called age hardening or particle hardening, is a heat treatment technique used to increase the yield strength of malleable materials, including most structural alloys of aluminium, magnesium, nickel, titanium, and some steels, stainless steels, and duplex stainless steel. In superalloys, it is known to cause yield strength anomaly providing excellent high-temperature strength. Precipitation hardening relies on changes in solid solubility with temperature to produce fine particles of an impurity phase, which impede the movement of dislocations, or defects in a crystal's lattice.
Colored gold
Colored gold is the name given to any gold that has been treated using techniques to change its natural color. Pure gold is slightly reddish yellow in color, but colored gold can come in a variety of different colors by alloying it with different elements. Colored golds can be classified in three groups: Alloys with silver and copper in various proportions, producing white, yellow, green and red golds. These are typically malleable alloys. Intermetallic compounds, producing blue and purple golds, as well as other colors.
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