| High strength with loss of ductility has been demonstrated a limitation of engineering utility in bulk nanostructured materials. Y.M.Wang et al reported nano-Cu with bimodal structure obtained by cryo-rolling at liquid nitrogen, which possess excellent tensile ductility without obvious loss of strength. It suggests micrometer-sized grains with some fractions embedded in nanostructured matrix, namely bimodal structure was possible to be an effective route to eliminate the loss of ductility. On the other hand, Chokshi et al founded complete different result in annealed electrodeposition nanometer crystal nickel,which is the same as the conditional recognition that the mixcrystal structure would deteriorate mechanical properties gravely.But as a typical kind of mixcrystal structure,bimodal improve the properties,which show that we should research the different two grain size's parameters deeply.And if we want to get the point,first job is to prepare the bimodal that structure's parameters is controllable.In this paper,it establish a new method to get the bimodal that structure's parameters is controllable successly in Cu-Al eutectoid system alloy by composition design + eutectoid-phase-transformation treatment + severe plastic deformation + annealing.Investigate the relation of structure and properties preliminary and verify the bimodal's feasibility.Results show that: we get the bimodal structure of micro grain pro-eutectoid phase+ultra grain-refining eutectoid matrix by ECAP+annealing processing chains in Cu-Al eutectoid system alloy; and the bimodal does improve the ductily, tensile ductility is greatly improved without much loss of strength.And the ductily increases with the pro-eutectoid's volume proportion and annealing temperature's increasing, At the condition of pro-eutectoid phase's volume proportion is 40%,ductility would be better when the pro-eutectiod phase's distribution is more uniform and litter,material would get the high strength and high elongation. |
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