Stacking Disorder and Annealing Behavior in the Heavily Deformed α₂ Phase of Cu–Al Alloys

Abstract

The stacking disorder in the filed α₂ phase af Cu–Al alloys was investigated by means of X-ray powder diffraction. The theoretical line profiles were calculated so as to reproduce the observed ones by using the diffraction theory of Kakinoki and Komura developed for one-dimensionally disordered structure. The values of the parameters in the diffraction equation, thus determined, indicate that the stacking mode in the filed α₂ phase can be characterized by a statistical mixing of 3R, 9R in a negative sequence, and 2H. The annealing behavior of the filed α₂ was examined and it was found that the filed α₂ decomposes to (α+γ₂), although the final stable state is the α₂ phase. The annealing behavior observed is quite similar to that of the filed β₁′ martensite of Cu–Al alloys.