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

A systematic creep study was undertaken for the binary intermetallic Al3Sc and the ternary single-phase intermetallic Al3(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 Al3Sc 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 Al3(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.