Period of Antiphase and Tetragonality in the α<SUB>2</SUB> Phase of Cu–Al Alloys

Abstract

A structural investigation on the α2 phase of Cu–Al alloys was performed by means of X-ray powder diffraction and electron microscopy. The α2 phase investigated was obtained by annealing the martensitic state of the alloy for a prolonged time. The electron diffraction pattern of the α2 phase indicated that the α2 phase has a one-dimensional long period superlattice (LPS) in agreement with the result obtained previously by other investigators. The change in the period of antiphase with the Al concentration was measured by means of X-ray diffraction, and it was concluded that Sato and Toth’s theory is valid for the α2 phase of the Cu–Al alloys. An unusual broadening of the line profile which was observed in the X-ray powder pattern of the α2 phase was analyzed to obtain the tetragonality of the fundamental face-centred lattice. The tetragonality was found to have a value of 1.002∼1.003 and to vary by a small amount with increasing Al content. The dependence of lattice parameters of the phase on the Al concentration was also determined.