BULK AND DISLOCATION CORE DIFFUSION IN AL-MO SOLID-SOLUTIONS OBTAINED THROUGH RAPID-SOLIDIFICATION PROCESSING

Samples of Al-2. 2 at. % Mo and Al-0. 7 at. % Mo have been prepared as solid solutions by melt-spinning, and have then been annealed at temperatures between 643 and 923 K. Analytical transmission electron microscopy has been used to determine the factors that control the rate of return to equilibrium in these supersaturated solid solutions. In the Al-2. 2 at% Mo alloy the diffusion of Mo, to form the equilibrium phase Al//1//2Mo, is accompanied by the formation of dislocation networks, which separate regions that contain 2. 2 at% Mo from regions of virtually pure Al. The dislocations accommodate the change in lattice parameter between these two regions and provide diffusion paths to grain boundaries, where Al//1//2Mo is precipitated. In the case of Al-0. 7 at. % Mo, diffusion occurs either along grain boundaries, during grain growth, or through the bulk of the grains, but no dislocations are generated during annealing. Measurements of the width of the denuded zones at stationary grain boundaries in this dilute alloy have been used to determine the kinetics of diffusion of Mo in Al.