Factors Influencing Tensile Ductility of OFHC Cu Having Different Ultrafine Grained Structures

Abstract

Tensile ductility of OFHC Cu with the different ultrafine grained (UFG) structures, which were fabricated by the different routes of equal channel angular pressing (ECAP), was associated in detail with the microstructural characteristics developed by ECAP. OFHC Cu having the lamellar and equiaxed UFG structures was prepared by ECAP of routes A and Bc, respectively up to 8 and 16 passes. Their microstructures were closely examined by transmission electron microscopy and orientation image mapping. Tensile tests at room temperature were conducted on the ECAPed samples under the quasi-static condition of 10 � 3 s � 1 and 1 s � 1 . Uniform elongation of the lamellar UFG samples decreased with increasing the ECAP passage while both uniform and total elongations of the equiaxed UFG samples increased. In the case of route A producing the lamellar UFG structure, the fractions of high angle grain boundaries and grains less than 0.5 mm increased significantly but an analysis revealed that the dislocation free length decreased with increasing the ECAP passage. For route Bc resulting in the equiaxed UFG structure, the fraction of high angle grain boundaries increased but the grain size distribution and the dislocation free length remained nearly unchanged with increasing the ECAP passage. From the present experiments and analyses, it was found that tensile ductility of lamellar UFG OFHC Cu is primarily controlled by the dislocation free length and that of the equiaxed one is mainly dependent on the fraction of high angle grain boundaries. [doi:10.2320/matertrans.M2010089]