CU-C AND AL-CU-C PHASE-DIAGRAMS AND THERMODYNAMIC PROPERTIES OF C IN THE ALLOYS FROM 1550-DEGREES-C TO 2300 DEGREES-C

The Cu-C and Al-Cu-C phase diagrams were determined at 1550-degrees-C to 2300-degrees-C by chemical and X-ray diffraction analyses of alloys saturated with carbon within sealed graphite crucibles. Isothermal sections for the ternary system were determined at intervals of 150-degrees-C over the range of temperatures investigated. The univariant points in atomic percent on the 1700-degrees-C, 1850-degrees-C, and 2000-degrees-C isotherms are 70.7Al-28.9Cu-0.4C, 74.4Al-24.0Cu-1.6C, and 78.3Al-17.0Cu-4.7C, respectively, as determined by metallographic examination of rapidly cooled alloys. Graphite and A14C3 (decomposition temperature 2156-degrees-C) were the only solid phases observed at these temperatures. The excess partial Gibbs energy for dissolved carbon in the liquid Al-Cu-C solutions in equilibrium with C, as calculated from the experimental solubilities, is G(c)eBAR = -RT In x = y2[176,860 - 55.42T - (224,200 - 110.84T)x] + z2[237,000 - 48.61T] + yz[320,510 - 36.77T + (30,180 + 35.10T)z + (51,570 - 74.13T)yz + (246,400 - 88.04T)yz2 - 60,000], J/g atom where R is the gas constant, T is the temperature in K, and x, y, and z are the atomic fractions of C, Al, and Cu, respectively. The equation also is a good approximation for liquid solutions in equilibrium with A14C3.