Thermodynamic Properties of Alloys of the Al-Co and Al-Co-Sc systems

Enthalpies of mixing for melts of the binary Al-Co system at 1870 K in the range 0 < x (Co) < 0.25, and at 1620 K, 0 < x (Co) < 0.12, are investigated by means of isoperibolic calorimetry. Enthalpies of mixing for melts of the ternary Al-Co-Sc system are investigated at 1870 K for sections Al0.75(1 - x)Co0.25(1 - x)Sc (x) , 0 < x < 0.024, and Al0.88(1 - x)Co0.12(1 - x)Sc (x) , 0 < x < 0.044. Using the literature data on the enthalpies of mixing for liquid and solid alloys, the activities of melt components, and the phase diagram of the Al-Co system, the thermodynamic properties of liquid and solid alloys of the Al-Co system over a wide range of temperatures and compositions are calculated using a software package of our own design, based on the model of ideal associated solutions (IAS). The enthalpies of mixing and the liquidus surface of the phase diagram of the ternary Al-Co-Sc system over the interval of concentrations are estimated by modeling with data on binary boundary subsystems. All of the components of both the binary Al-Co and ternary Al-Co-Sc systems tend to interact with one another quite strongly: Delta H (min)(Al-Co) = -32.5 kJ/mol at x (Co) = 0.44; Delta H (min)(Al-Co-Sc) = -46 kJ/mol for Al0.4Co0.3Sc0.3 (estimated).