Elucidating the deformed behaviors and strengthening mechanisms in Cu alloys with bimodal structure

Designing heterogeneous structures in metallic materials has been reported to alleviate the paradox of strength and ductility. In the present work, Cu alloys with a bimodal grain structure were obtained by cold rolling and subsequent short annealing (500 degrees C for 10min). Tensile properties results showed that the bimodal grain structure sample exhibited 1.5 times higher yield strength and almost the same ductility as compared to the homogeneous coarse grain sample. In addition, extra strengthening and apparent heterogeneous deformationinduced (HDI) effect were observed in the bimodal grain structure sample. At the low strain stage, abundant dislocations were accumulated near the coarse grain at the interface of coarse grain and fine grain, which contributed to extra strengthening. At the tensile strain of 10 %, dislocation slip was dominated and a few deformation twins were activated near the fine grains while abundant dislocations, stack faults and deformation twins were activated near the coarse grains, which indicated that there was the strain accommodation at the interface of coarse grain and fine grain. Furthermore, the EBSD results indicated that there was strain partitioning between the fine grain and coarse grain. A superior strength-ductility synergy in the bimodal grain structure sample mainly derived from heterogeneous grains and the HDI strengthening. This work provides insight into the deformation behavior and strengthening mechanism of bimodal grain structure.