Thermodynamic Solidification Path Assessment and Microstructural Comparison of Deep Eutectic Au-Cu-Si System

Particularly in karat gold alloys in jewelry applications, many alloy formulations include a small amount of silicon for filigree castings and brightening effect [1]. On the other hand, some alloy manufacturers stayed away from silicon or set a maximum amount of silicon to avoid embrittlement [1-3]. However recent development of gold-based bulk metallic glass involved a large addition of silicon (16.3 at% Si) in the alloy formulation [4-6]. No silicon segregation had been observed in large ingots that were cooled at 100 K/s and above. In the current study of Au55Cu25Si20 alloy, extra silicon has been added to investigate the segregation effect using three different techniques for cross references: equilibrium solidification path, Scheil-Gulliver solidification with ThermoCalc® and microstructural study with varying cooling rates. The amounts of solidified primary and eutectic silicon were measured in three differently cooled ingots. Image analysis using ImageJ® was used to obtain size distributions, area fractions, and volume fractions of silicon in both primary silicon and eutectic silicon.