Фазовая диаграмма системы Cu-Hf

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Cu-Hf (Copper-Hafnium) P.R. Subramanian and D.E. Laughlin The equilibrium phases of the assessed Cu-Hf phase diagram are (1) the liquid, L; (2) the fcc terminal solid solution (Cu), with a maximum solid solubility of ~0.4 at.% Hf; (3) the intermediate phase Cu5Hf, with an undetermined crystal structure, stable up to the peritectic melting temperature of 1055 C; (4) the Ag51Gd14-type hexagonal intermediate phase Cu51Hf14, stable up to the congruent melting point of ~1115 C; (5) the orthorhombic phase Cu8Hf3 with a new prototype crystal structure, stable up to the peritectic temperature of 990 C; (6) the orthorhombic Ni10Zr7-type intermediate phase Cu10Hf7, stable up to the congruent melting temperature of ~1025 C; (7) the tetragonal MoSi2- type intermediate phase CuHf2, stable up to the congruent melting temperature of 1310 C; (8) the hexagonal Mg-type terminal solid solution, (aHf), stable up to 1743 C and having a maximum solid solubility of 0.9 at.% Cu at 1540 C; and (9) the cubic W-type terminal solid solution, (bHf), stable between 1540 and 2231 C and having a maximum solid solubility of ~4.3 at.% Cu. The assessed phase diagram is based on review of the work of [67Wat], [74Mar], [74Per], [74Pie], [75Bse], [75Gab], and [76Bse]. The diagram was calculated using thermodynamic data. The following assumptions were made: (1) the solid phases (Cu) and (aHf) have no significant solid solubilities; (2) the lattice stability parameters for Cu and bHf are derived from the enthalpies of fusion as well as the melting points of the respective elements; the lattice stability parameter for aHf is derived from that of bHf as well as from the enthalpy and temperature of the a = b transformation; and (3) all of the intermediate phases are line compounds, i.e., the phases show negligible homogeneity ranges. Liquidus boundary calculations were not successful for the Hf-rich end of the diagram, primarily because of the scarcity of experimental liquidus and thermodynamic data within the composition range 75 to 100 at.% Hf. Moreover, the solidus and solvus boundaries for (bHf) are not known within reasonable confidence levels. Therefore, the present evaluators consider the Hf-rich end of the Cu-Hf phase diagram tentative and in need of further experimental research. Although a majority of studies showed the Cu-rich terminal eutectic to lie between 950 and 970 C, it has been accepted as 988 C from [74Per], because this was based on thermal arrest data from at least eight alloy compositions, and taken during both heating and cooling. The accepted maximum solid solubility of ~0.4 at.% Hf at 988 C was obtained by extrapolation of the solubility data of [67Wat]. Only limited information is available on the solubility of Cu in (Hf). [74Pie] estimated the solubility of (aHf) to be ~0.3 at.% Cu and ~0.9 at.% Cu at the invariant temperatures of 1295 and 1540 C, respectively. The maximum solid solubility in (bHf) was estimated by [74Pie] to be ~4.3 at.% Cu at the metatectic temperature of 1540 C. 62Nev: M.V. Nevitt and J.W. Downey, Trans. Metall. AIME, 224, 195-196 (1962). 67Wat: R. Watanabe, Trans. Natl. Res. Inst. Metals (Tokyo), 9(1), 13-19 (1967). 74Mar: V.Y. Markiv, V.V. Pet'kov, A.I. Storozhenko, V.G. Ivanchenko, and V.V. Gorskiy, Izv. Akad. Nauk SSSR, Metall., 2, 209-213 (1974) in Russian; TR: Russ. Metall., 2, 123-125 (1974). 74Per: A.J. Perry, Mater. Sci. Eng., 13, 57-62 (1974). 74Pie: B. Pieraggi, F. Dabosi, and M. Armand, J. Nucl. Mater., 52, 336-338 ( 1974) in French. 75Bse: L. Bsenko, J. Less-Common Met., 40, 365-366 (1975). 75Gab: J.P. Gabathuler, P. White, and E. Parthe, Acta Crystallogr. B, 31, 608- 610 (1975). 76Bse: L. Bsenko, Acta Crystallogr. B, 32, 2220-2224 (1976). 79Ess: R.M. Van Essen and K.H.J. Buschow, J. Less-Common Met., 64, 227-284 ( 1979). Published in Bull. Alloy Phase Diagrams, 9 (1), Feb 1988. Complete evaluation contains 1 figure, 8 tables, and 17 references. Special Points of the Cu-Hf System