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

Mechanical alloying was used to prepare powders of copper-niobium allo ys containing between 10% and 28% by volume of niobium which were subs equently consolidated by hot compaction or extrusion. Materials contai ning higher niobium contents are stronger in the powder state and afte r annealing at lower temperatures but are less stable at high temperat ures than the more dilute materials examined here and these concentrat ed alloys soften faster during high temperature annealing. Strengtheni ng in the powder state is affected by the extensive work hardening int roduced by the milling process but after consolidation the strength is mostly determined by Orowan-type dislocation pinning by fine particle s. Milling powders, even for extended time periods, is not able to ref ine all the added niobium to the optimum nanometre scale and the remai ning coarser niobium leads to faster microstructural coarsening during high temperature annealing.