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

Abstract

AbstractÐA systematic creep study was undertaken for the binary intermetallic Al 3 Sc and the ternary single-phase intermetallic Al 3 (Sc 0.74 X 0.26 ), 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 Al 3 Sc exhibits a stress exponent of 4.4±4.9 indicative of creep controlled by climb of dislocations. The activation energy for creep of Al 3 Sc was 12826 kJ/mol, close to that for self-di usion for pure aluminum, in agreement with the Cu 3 Au rule, indicating that di usion on the Al-sublattice is controlling. Ternary Al 3 (Sc 0.74 X 0.26 ) 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 2 8 kJ/mol were found, showing that ternary substitution for scandium with transition metals a ects di usion on the Al sublattice. 7

Microstructure and Hardness of Scandium Trialuminide with Ternary Rare-Earth Additions

“…[11] (no significant Sm difference was found in the correlation when ionic Pauling's radii were used). A similar correlation was found by Yamamoto et al [12] for the L1 2 quaternary phase {(AlMn) 3 Ti} (1-n) X n , where X is =Zr, V, Ag or, Ga. This correlation can be understood in terms of the size mismatch associated with the replacement of solvent atoms with solute atoms causing a distortion of the lattice.…”

“…In an earlier paper [3], we investigated the compressive creep behavior for Al 3 (Sc 0.74 TM 0.26 ), where TM is one of the transition-metal of Ti, Y, Zr or, Hf. At 873 K, a decrease in creep rates of one order of magnitude was found for Zr and Hf, and two orders of magnitude for Ti and Y.…”

“…Scandium trialuminide, Al 3 Sc, is of interest because of its low density (3.03 Mg m -3 ), relatively high melting point (1593 K) and potentially useful high-temperature strength. Al 3 Sc has the cubic L1 2 structure which is expected to show enhanced ductility, because of the high crystallographic symmetry and thus, the high number of possible slip systems.…”

“…Al 3 Sc has the cubic L1 2 structure which is expected to show enhanced ductility, because of the high crystallographic symmetry and thus, the high number of possible slip systems. Despite its L1 2 structure, polycrystalline Al 3 Sc is brittle at room temperature [1]. Partial substitution of Sc by other elements may increase the ductility of Al 3 Sc and also decrease the cost of the alloy.…”

“…However, very little is known about the alloying behavior of Al 3 Sc, with the exception of a recent study investigating the solubility limit of the transition metals (TM) Y, Ti, Zr, Hf, V, Nb and Ta [2]. It was found that solid-solution strengthened Al 3 (Sc 1-y TM y ) showed improved creep properties as compared to binary Al 3 Sc [3]. The alloying behavior of Al 3 Sc is also important for the rational design of Sc-containing aluminum alloys, in which small volume fractions of coherent Al 3 Sc particles are precipitated [4].…”