Mechanical Alloying Processing with Application to Structural Materials: ASSERT Supplement

When two-phase mixtures of ductile metals are mechanically alloyed, they often assume a convoluted lamellar structure. Since these powders are consolidated elevated temperatures, their structures and therefore properties are likely be altered by consolidation processing. We have investigated microstructural changes that take place on heat-treating mechanically alloyed Cu-20 vol. NB alloys. The transition from a Plate-like to a spherical microstructure is described and the kinetics of this process appear controlled by a type of boundary diffusion even though the coarsening temperature was high in terms of the homologous temperature of Cu. Reasons for this behavior are suggested. Finally, during heat treatment carried out in hydrogen, a Nb layer forms around the particles. The thickness of this layer and the corresponding zone denuded of Nb within the particle increases with continued elevated temperature exposure, and at a rate consistent with the process being driven by curvature forces.