Stability and elastic properties of L1 2-(Al,Cu) 3(Ti,Zr) phases: Ab initio calculations and experiments

Abstract

The total energies and equilibrium cohesive properties of L1 2, DO 22 and DO 23 structures along Al 3Ti–Al 3Zr and Al 3X–Cu 3X (X = Ti, Zr) sections are calculated from first principles employing electronic density-functional theory (DFT), ultrasoft pseudopotentials and the generalized gradient approximation. Calculated heats of formation are consistent with a narrow field of stability of the L1 2 structure at 12.5 at.% Cu for ternary (Al,Cu) 0.75Zr 0.25 and (Al,Cu) 0.75Ti 0.25 intermetallics at low temperatures. Experimentally, samples homogenized at 1000 °C establish a more extensive stability field for the L1 2 phase in quaternary alloys with Cu concentrations ranging from 6.7 to 12.6 at.% Cu. Two L1 2 phases were observed in as-cast alloys with near equal amounts of Ti and Zr, as well as alloys homogenized at 1000 °C. Good agreement is obtained between calculated and measured values of lattice parameters and elastic moduli. These results demonstrate high accuracy of ab initio calculations for phase stability, lattice parameters and elastic constants in multicomponent trialumide intermetallics.