Gold-Palladium-Tungsten - (Ping Liang)
Introduction
[72Jon] constructed isothermal sections of the Au-Pd-W system at 1450C and 1200C to examine the use of Au-Pd alloy coatings for the protection from oxidation of the refractory metal W. The ternary alloys were prepared by melting the elements in an induction furnace under argon or, for W-rich alloys in an argon-arc furnace. The alloys were homogenized for not less than 65 h at the relevant temperatures and water quenched. The phase boundaries were determined by conventional metallography. The phase composition of two-phase alloys were obtained by X-ray determination of the lattice parameters. Two tie lines were established at each of the relevant temperatures.
Binary Systems
According to [Mas2] the Au-Pd system consists of a continuous series of solid solutions, with liquidus and solidus curves rising smoothly from the melting point of Au to that of Pd. A tentative phase diagram is given for the Au-W system with a eutectic formed at 0.1 at.% W and 1063C [Mas2]. The Pd-W phase diagram presented by [Mas2] is redrawn from [S].
Solid Phases
No ternary compounds have been reported. The only solid phases in the ternary system are the (Au,Pd) solid solution (fcc) and the restricted solid solution of Pd in W (bcc). The crystallographic data are given in Table 1.
Isothermal Sections
Figure 1 and Fig. 2 show the isothermal sections at 1450C and 1200C mainly based on the experimental determination of the (W)/(W)+(Au,Pd) boundaries by [72Jon].
Miscellaneous
[69Pra] investigated the effect of W on the physical and mechanical properties of the Au-Pd alloys and proposed a phase diagram for an unspecified temperature described as near to room temperature. The diagram, based on metallographic examination of alloys annealed for 100 h at 1000C and slowly cooled, shows the equilibrium between (W) and the (Au,Pd) solid solution containing W. The convexity of the ternary boundary towards the Pd corner of the diagram is less pronounced than in Fig. 1 and Fig. 2. The diagram is not reproduced since the temperature it refers is not known; it does, however, confirm the general nature of the equilibria.
References
[69Pra]
N.L. PRAVOVEROV and I.S. BEGATOVA, "On the Structure and Properties of Some Alloys of the Au-Pd-W System", Izv. Akad. Nauk SSSR, Met., 6, 177-180 (1969) (Equi. Diagram, Experimental, 3)
[72Jon]
B. JONES, M.W. JONES and D.W. RHYS, "Precious-Metal Coatings for the Protection of Refractory Metals", J. Inst. Met., 100, 136-141 (1972) (Equi. Diagram, Experimental, 27)
Phase/ | Pearson | Lattice | Comments |
(Au,Pd) | cF4 | a = 407.82 | pure Au, 25C [Mas2] |
(W) | cI2 | a = 316.52 | pure W, 25C [Mas2] |
