Microstructural evolution of Au–35 mass% Ag–15 mass% Cu alloy during ageing at 415 °C

• Published in: Journal of thermal analysis and calorimetry Vol. 146; no. 6; pp. 2343 - 2351
• Main Authors: Amiour, L., Hamana, D., Chetibi, L.
• Format: Journal Article
• Language: English
• Published: Cham Springer International Publishing 01.12.2021; Springer; Springer Nature B.V
• Subjects: Aging (metallurgy); Alloys; Analytical Chemistry; Calorimetry; Chemical precipitation; Chemistry; Chemistry and Materials Science; Copper; Copper base alloys; Crystal structure; Crystallinity; Crystals; Diffraction; Gold; Grain boundaries; High resolution electron microscopy; Inorganic Chemistry; Measurement Science and Instrumentation; Microscopy; Optical microscopy; Order-disorder transformations; Phase diagrams; Phase transitions; Physical Chemistry; Physical properties; Polymer Sciences; Silver; Solid solutions; Specialty metals industry; Structure; Ternary systems; X-ray diffraction; X-rays; Cellular precipitation; SEM; Ageing; Au–Ag–Cu alloy; Ordered phase; HRTEM
• ISSN: 1388-6150; 1588-2926
• DOI: 10.1007/s10973-020-10204-0

The thermal analyses of Au–35 mass% Ag–15 mass% Cu alloy show different phase transformations (order-disorder transition and precipitation reaction) which have not been well identified before. It is known that the physical properties of this alloy depend on the crystalline and microstructural changes. Thus, to identify all phases optical microscopy, X-ray diffraction (XRD), differential scanning calorimetry, scanning electron microscopy and high-resolution transmission electron microscopy are used. Moreover, the crystalline structure of the formed phases has been followed by XRD, elemental X-ray mapping and electronic diffraction. These techniques show for the first time, the simultaneous occurrence of discontinuous precipitation and disorder-order transition during ageing at the same temperature 415 °C. Indeed, cells with lamellae of Ag-rich α 1 and Cu-rich α 2 solid solutions and AuCu 3 -ordered phase are, respectively, formed at grain boundaries by discontinuous decomposition of Ag-rich α 1 supersaturated solid solution and in the grain interior of the α 0 parent Au-rich phase. The presence of a third phase—Cu-rich α 2 solid solution—is revealed in the ternary Au–Ag–Cu phase diagram at 400 °C isothermal section.