Ordering and Disordering Processes inCu3Au. I

Abstract

Data are reported which describe the isothermal change of Young's modulus with time in a single crystal of ${\mathrm{Cu}}_3$Au following a sudden change in temperature below the critical temperature when a specimen is initially in various states of equilibrium long-range order. The results are compared with a modification of the kinetic theory of ordering and disordering proposed by Rothstein and Dienes. It appears that both processes proceed in two distinct but merging stages, one of which is described well by the theory in each case. The other is plausibly ascribed to the growth and dissolution of isolated clusters of disordered atoms, similar to those deduced by Chipman from x-ray evidence. Phenomena observed in the immediate neighborhood of the critical temperature occur when these clusters are sufficiently large and numerous to be contiguous.