Formation of AB2-intermetallics by diffusion in the Au-Sb-Bi system

Binary diffusion couples, in which one single-phased product layer is growing between pure elements, were employed to study the diffusion properties of Au2Bi- and AuSb2-intermetallics at 230 and 330 DegC. The position of the Kirkendall-marker plane inside the reaction zones revealed that in this temp. range the minority element is the faster diffuser in the Laves-phase Au2Bi as well as in AuSb2. The concept of the integrated diffusion coeff. is used to describe the growth kinetics of the intermetallic compds. The integrated diffusion coeff. in an intermetallic is related to the tracer diffusivities of the components and the thermodn. stability of the phases involved in the interaction. The tracer diffusion coeffs. were deduced from the interdiffusion expts. The isothermal cross-section through the ternary phase diagram Au-Sb-Bi at 230 DegC was constructed using the diffusion couple technique. No ternary phases are found in this system. Both intermetallic compds. Au2Bi and AuSb2 are in equil. with the (Sb,Bi)-solid soln. The soly. of Sb in the Laves-phase Au2Bi was found to be negligible. Up to about 10.5 at.% of Bi can be dissolved in the AuSb2-phase, the Bi-atoms substituting for Sb in the cubic lattice of AuSb2.