PERIOD OF ANTIPHASE AND TETRAGONALITY IN ALPHA2 PHASE OF CU-AL ALLOYS

A structural investigation of the alpha //2 phase of Cu-Al alloys was performed by x-ray powder diffraction and electron microscopy. The phase was obtained by annealing the martensitic state of the alloy for a prolonged time. The electron diffraction pattern indicated that the alpha //2 phase had a one-dimensional long period superlattice (LPS) in agreement with the findings of others. The change in the period of antiphase with Al concentration measured by x-ray diffraction showed that H. Sato and R. S. Toth's theory is valid for the alpha //2 phase of the Cu-Al alloys. An unusual broadening of the line profile which was observed in the x-ray powder pattern of the alpha //2 phase was analyzed to obtain the tetragonality of the fundamental face-centered lattice. The tetragonality was found to have a value of 1. 002 to about 1. 003 and to vary by a small amount with increasing Al content. The dependence of the lattice parameters of the alpha //2 phase on Al concentration was also determined.