Element partitioning during coarsening of (gamma-gamma') Ni-Al-Mo alloys

The coarsening rate constants of several Ni-Al-Mo ternary alloys are examined at 842 °C, 872 °C and 903 °C. Arrhenius plots of the coarsening rate constants provide strong experimental indication for a change in the rate-controlling mechanism for coarsening from the long-range diffusion of Al to the long-range diffusion of Mo. This is supported by an estimate of the relative contributions of the alloying elements, Al and Mo, to the overall coarsening resistance of the alloys. The increased apparent activation energy of coarsening in the high Mo alloy is considered strong evidence that a change in the rate-controlling mechanism of coarsening from long-range diffusion of Al to long-range diffusion of Mo occurs in this series of alloys.