Layer growth in diffusion couples, which consisted of Al thin films and bulk Au, was studied at temperatures ranging from 523 to 773K by means of scanning electron microscopy, electron probe micro-analysis and optical microscopy. The results showed that, before the disappearance of the Al thin film, 5 intermetallic phases (as seen in the phase diagram) formed in the couple. After the disappearance of the Al film, phases with a lower Au content disappeared in sequence. Following the disappearance of Al2Au, AlAu and Au2Al, the Au4Al phase grew in Au5Al2. Kirkendall voids formed in the Au5Al2; adjacent to Au4Al. It was found that the addition of a small amount of Ca to the bulk Au made the voids smaller, and facilitated diffusion; thus promoting the growth of Au4Al.

M.Hanai, M.Houkyou, N.Utiyama, A.Fuwa: Journal of the Japan Institute of Metals, 1996, 60[1], 37-43