Creep properties of Al3Sc and Al3(Sc, X) intermetallics

A systematic creep study was undertaken for the binary intermetallic Al3Sc and the ternary single-phase intermetallic Al-3(Sc0.74X0.26), where X is one of the transition-metals Ti, Y, Zr or Hf. Creep tests were conducted in the temperature range from 673 to 1200 K under a constant compressive stress ranging from 30 to 300 MPa. The binary Al3Se exhibits a stress exponent of 4.4-4.9 indicative of creep controlled by climb of dislocations. The activation energy for creep of Al3Sc was 128 +/- 6 kJ/mol, close to that for self-diffusion for pure aluminum, in agreement with the Cu3Au rule, indicating that diffusion on the Al-sublattice is controlling. Ternary Al-3(Sc0.74X0.26) exhibits a decrease in creep rate by about one order of magnitude for Zr and Hf and by about two orders of magnitude for Ti and Y. For all ternary alloys, a stress exponent of 3.9-5.5 was observed, indicative of dislocation creep. Activation energies for creep of 202 +/- 8 kJ/mol were found, showing that ternary substitution for scandium with transition metals affects diffusion on the Al sublattice. (C) 2000 Acta Metallurgica Inc. Published by Elsevier Science Ltd. AN rights reserved.