The phase relations in the Au-Ni-Sn system have been ex-Samples were made by melting (heating at 1100-1300ЊC amined by powder X-ray diffraction, metallography, electron microprobe analysis, and thermal analysis. The range of homo-for ca. 1 min under vigorous shaking) weighed amounts geneity of the various phases, tie-lines, and tie-triangles are of 99.95% Au (Rasmussen), 99.98% Ni (Goodfellow), presented for an isothermal section of the phase diagram at and 99.98% Sn (Merck) in sealed, evacuated, silica-glass 400؇C. Au and Ni can scarcely be mutually exchanged in most of tubes. This initial heat treatment was in most cases the phases, but a continuous range of solid solubility seemingly concluded by quenching the samples from the molten occurs between AuSn (␦) and Ni 3 Sn 2 (␥). The maximum variastate into water, otherwise cooled slowly to room tempertion in the Sn content for this phase is found to be ca. 5 at%, ature. Most samples were then annealed at 400ЊC (for for mole fractions between n Ni /(n Au ؉ n Ni ) ؍ 0.7 and 1.0. The 2-7 days) and then quenched into water. The Ni-rich only genuine ternary phase in the system, labeled A, takes the samples were annealed for a minimum of 7 days because virtually stoichiometric composition AuNi 2 Sn 4 and exists at of the high melting temperatures in this region of the 400؇C.