Thermodynamic measurements and assessment of the Al-Sc system

A study of the binary AI-Sc phase diagram has been performed by means of thermodynamic calculations and experimental measurements. The enthalpy of formation of all intermetallic compounds has been determined and a cursory examination of the phase equilibria carried out, for compositions greater than 40 at% Sc. Two new invariant reactions have been identified in the Sc-rich part of the diagram: L <-> (beta Sc)+ Sc2Al at 1185 degrees C and (beta Sc) <-> Sc2Al+(alpha Sc) at 970 degrees C. A coherent set of Gibbs energy expressions for all the phases in the system has beep generated by a least square optimisation procedure using all the experimental data available. The overall agreement is satisfactory but some uncertainties still persist, especially concerning the ScAl phase, owing to experimental difficulties. (C) 1998 Elsevier Science Ltd. All rights reserved.