MICROSTRUCTURE AND MECHANICAL-PROPERTIES OF CONCENTRATED COPPER NIOBIUM ALLOYS PREPARED BY MECHANICAL ALLOYING

Mechanical alloying was used to prepare powders of copper-niobium alloys containing between 10% and 28% by volume of niobium which were subsequently consolidated by hot compaction or extrusion. Materials containing higher niobium contents are stronger in the powder state and after annealing at lower temperatures but are less stable at high temperatures than the more dilute materials examined here and these concentrated alloys soften faster during high temperature annealing. Strengthening in the powder state is affected by the extensive work hardening introduced by the milling process but after consolidation the strength is mostly determined by Orowan-type dislocation pinning by fine particles. Milling powders, even for extended time periods, is not able to refine all the added niobium to the optimum nanometre scale and the remaining coarser niobium leads to faster microstructural coarsening during high temperature annealing.