Phase formation in the diffusion couple of aluminum thin film and gold bulk and the influence of calcium on the phase formation

The behavior of phase layer growth in the diffusion couple of aluminum thin films and gold bulks at the temperatures from 523 K to 773 K was studied by means of SEM, EPMA and optical microscopy. The effect of calcium addition on phase layer growth was also studied. The experimental results show: before the disappearance of aluminum thin films, five intermetallic phases in its equilibrium phase diagram form in the couple and after the aluminum disappearance, the phases with a lesser gold content disappear in sequences. After the disappearance of the AuAl₂, AuAl and Au₂Al phases, the Au₄Al phase grows in the Au₅Al₂. Kirkendall voids are found to form in the Au₅Al₂, adjacent to Au₄Al. The addition of a small amount of calcium to the Au bulks affects the morpohology, making void sizes smaller and diffusion easier, thus promoting the growth of the Au₄Al phase.