Phase stability investigations of the palladium-cadmium system: part ii. structural studies
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I.
INTRODUCTION
THE thermodynamic
properties of palladium-cadmium alloys have been investigated recently by Maa, Mikula, Chang, and Schuster t using isopiestic methods. The results of these studies cast some doubt on the correctness of parts of the Pd-Cd phase diagram presented by Hansen and Anderko; 2 it is the purpose of the present investigation to clarify this question. The outline of the Pd-Cd phase diagram by [2] is based on the work of Nowotny, Stempfl, and Bittner. 3 The region of the phase diagram that is pertinent to the thermodynamic investigations by [1] is shown in Figure 1. According to this diagram, at 1073 K (800 ~ the a-phase, a solid solution of Cd in Pd having the fcc structure, extends from pure palladium to approximately XCd = 0.26. A/3~-phase* with
I00(
-tog 60C 5(3(3 0.0
0.1
02
04
03 X
05
0.6
07
cd
Fig. l - - P a r t i a l phase diagram Pd-Cd, adopted from Hansen and Anderko -"
*The fl~-phase is designated a ' by [2] and ~5 by [3].
the fct L10 structure extends from Xcd = 0.33 to 0.49 and an a"-phase,* having a crystal structure similar to the/3rphase, *The a"-phase is designated 3' by [3].
is thought to exist from XCd = 0.51 to 0.53. The homogeneity range of the adjacent fl'-phase,* which has an
In order to resolve these discrepancies, selected samples from the isopiestic experiments were analyzed by X-ray diffraction to identify the intermetallic phases that are present and to determine their precise lattice parameters.
*The/3'-phase is designated/3 by [2] and [3].
ordered bcc B2 structure, extends from Xcd = 0.54 to 0.57. The thermodynamic studies confirm the position of the Pd-rich phase boundary of the fit-phase at Xcd = 0.33, but they are not in agreement with the above given phase boundaries near the equiatomic composition. In particular, no evidence for the existence of the a"-phase was found and indications are that the /31-phase extends beyond the equiatomic composition. J. P. NEUMANN is Associate Professor of Metallurgical Engineering, Department of Chemical and Metallurgical Engineering, University of Alabama, University, AL 35486. A. MIKULA is with Institut fiir Anorganische Chemie, Universitat Wien, Vienna, Austria. Y. A CHANG, formerly Professor of Materials Engineering and Associate Dean for Research, Graduate School, University of Wisconsin-Milwaukee, is now Professor of Metallurgical Engineering, Department of Metallurgical and Mineral Engineering, University of Wisconsin-Madison, 1509 University Avenue, Madison, WI 53706. Manuscript submitted April 23, 1981. METALLURGICAL TRANSACTIONS A
II. E X P E R I M E N T A L M E T H O D S AND RESULTS The determination of the precise lattice parameters was carried out by means of the same general methods described in the investigation of the Pd-Zn system. 4 The Pd-Cd samples, available from the isopiestic experiments t in the form of foils, were ground in a mortar to a particle size less than 45 gin. The ground samples were sealed in evacuated (10-tPa) quartz capsules, annealed for one day at 1073 K, and quenched i
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