Фазовая диаграмма системы Au-Pr

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Au-Pr (Gold-Praseodymium) K.A. Gschneidner, Jr., F.W. Calderwood, H. Okamoto, and T.B. Massalski The Pr-Au system is characterized by the existence of five compounds. The assessed phase diagram is based primarily on review of the work of [34Ros], [ 71Gri], and [71Mcm]. The melting point of pure Au has been adjusted from 1063 C, as shown in all of the phase diagrams observed for the Pr-Au system, 1064. 43 C, to agree with [Melt]. [71Gri] reported that the eutectic between (aPr) and the Pr-rich compound, Pr2Au, occurs at 619 с 1 C and 17.7 с 0.1 at.% Au. The a = b transformation temperature of Pr was lowered 43 C, and the solubility at the catatectic temperature of (bPr) = (aPr) + L is 1.56 с 0.05 at.% Au. The temperature for the a = b transformation in Pr has been corrected from 800 to 795 C. Consequently, the temperature for the catatectic reaction (bPr) = ( aPr) + L has been revised from 757 с 1 to 752 с 1 C. Pr2Au forms peritectically at 710 C from the melt and bPrAu, as shown by [ 34Ros]. Dashed lines for the liquidus between PrAu and ~90 at.% Au reflect the uncertainty concerning the reliability of the reported data [34Ros]. No other research was found to confirm the liquidus, melting temperature, eutectics, and the various horizontals in this region of the system. No temperature was found for the a = b transformation of PrAu2. [69Don1] and [69Don2] reported the existence of Pr14Au51 at 78.46 at.% Au with a melting temperature of ~1200 C. The compound PrAu6 at 85.7 at.% Au has been added to the assessed diagram. Peritectic formation of PrAu6 fromPr14Au51 and the melt at a temperature above 808 C is postulated. The Au-rich eutectic, then, would occur between PrAu6 and (Au) at about 808 C and at some composition between 86 and 90 at.% Au. [63Cha] found that intermediate phases of binary systems containing equiatomic amounts of Au with each of certain rare earth metals crystallize in the cubic CsCl-type structure. To obtain this structure for PrAu, it was necessary to rapidly quench from the molten state, an indication that this is a high- temperature form that transforms to another polymorphic form on slow cooling. [71Mcm] reported the melting point of PrAu to be 1415 с 10 C. They found that this phase exists in three modifications: an orthorhombic FeB-type structure that transforms to another orthorhombic form having the CrB-type structure at 550 с 5 C on heating and 430 с 5 C on cooling. The equilibrium transformation temperature is assumed by the present evaluators to lie halfway between these two values at 490 C. The CrB-type form undergoes a transition at 1340 с 10 C to a cubic CsCl-type structure. The melting temperature for PrAu and the a = b and b = g transformation temperatures in the assessed diagram are from [71Mcm]. [71Mcm] found PrAu2 to be polymorphic, crystallizing in an orthorhombic CeCu2- type structure at low temperatures and in a tetragonal NdAu2-type structure at high temperatures. No transformation temperature was reported. They also found that Pr14Au51 forms with a hexagonal structure. Metallographic examination revealed that a single phase exists at 78.7 at.% Au. [71Mcm] also verified the existence of PrAu6, but could not obtain single crystals of this compound or of the isotypic REAu6 phases. [71Gri] estimated the solubility of Au in (aPr) to be <0.12 at.% at 619 C and <0.1 at.% at 598 C. X-ray powder patterns of 18.8 and 33 at.% Au alloys showed that the Pr-rich compound in equilibrium with (aPr) is Pr2Au, which has the orthorhombic Co2Si-type structure. [34Ros] estimated the solubility of Pr in (Au) to be approximately 0.55 at.%, but in view of the results of [65Rid], this value is too high. A more realistic value would be ~0.1 at.% Pr. 34Ros: A. Rossi, Gass. Chim. Ital., 64, 748 (1934). 63Cha: C.C. Chao, H.L. Luo, and P. Duwez, Jr., J. Appl. Phys., 34, 1971 (1963). 65Rid: P.E. Rider, K.A. Gschneidner, Jr., and O.D. McMasters, Trans. AIME, 233, 1488 (1965). 69Don1: C. Donolato and S. Steeb, J. Less-Common Met., 18, 312 (1969). 69Don2: C. Donolato and S. Steeb, J. Less-Common Met., 18, 442 (1969). 71Gri: R.B. Griffin and K.A. Gschneidner, Jr., Metall. Trans., 2, 2517 (1971). 71Mcm: O.D. McMasters, K.A. Gschneidner, Jr., G. Bruzzone, and A. Palenzona, J. Less-Common Met., 25, 135 (1971). Published in Phase Diagrams of Binary Gold Alloys, 1987. Complete evaluation contains 3 figures, 2 tables, and 14 references. 1