Ordered phase formation and diffusion composition path in Cu 3Au/Pd couple

Abstract

EDX-TEM technique, IKL-ALCHEMI and Monte Carlo simulation were employed to reveal the relation between diffusion composition path and the ordered structures in Cu 3Au/Pd diffusion couple annealed at 573 K. A Cu 3Au layer including Pd, a CuAu layer including Pd, a CuPd layer and a Pd layer including Cu existed in sequence between Cu 3Au and Pd. The Au concentration increased by up-hill diffusion from the Cu 3Au layer to the CuAu layer, whereas Au scarcely diffused from the CuAu into the CuPd layer. The diffusion composition path deviated from the Cu 3Au–Pd line in the Cu–Au–Pd Gibbs triangle and exhibited an ‘S-shaped’ curve through the CuAu and CuPd existence regions. The atomic configurations in the L1 0-type phase were highly ordered and consistent with the equilibrium state. In the Monte Carlo simulation, diffusion couples were virtually produced. The diffusion composition paths, Fourier power spectra and Warren-Cowley parameters were estimated in this way. The strong ordering interactions of the Cu–Au pair and Cu–Pd pair in the first nearest neighbor and the high activation barrier for migration of Au reproduced experimental results.