Lattice matching of D0(23) and D0(22) phases in Al-6at%(Ti,V,Zr) systems

Abstract

Composite quaternary alloys with 21-22 vol.% of Al3M (M = Ti,V,Zr) were made by vacuum are melting. Two intermetallic phases were found in alloys: one is V rich D0(22)-Al-3(Ti,V,Zr) and the other is Zr rich D0(23)-Al-3(Ti,V,Zr). Measured lattice constants of precipitate phases were strongly dependent on the composition of transition elements in precipitates and generally obeyed Vegard's rule. The lattice misfits between Al3M phases and the matrix did not change much in alloys while the lattice misfit between D0(22) and D0(23) Al3M phases was found to decrease with an increase in Ti content implying that the interface between both phases became more smooth, hard to distinguish and separate. A geometrical model was made for the lattice matching between two, D0(22) and D0(23) Al3M phases. Titanium has been found to act as a retarding element to separation into D0(23) and D0(22) phases and the pre-existing phase may have been L-12 or D0(23) phase. (C) 1997 Elsevier Science S.A.