Microstructure evolution and mechanical property of nanocrystalline Ni-20Fe alloy during cold rolling

We report the microstructure evolution and mechanical property during room-temperature rolling of nanocrystalline Ni-20Fe alloys. The results show that massive dislocations and deformation twins in the deformed samples. Quantitative x-ray analysis reveals deformation induced grain rotation and grain growth. The dislocation density increases firstly and then tend to saturation after an equivalent strain (epsilon(VM)) of similar to 0.10 during the deformation. Correspondingly, the hardness increases when the epsilon(VM) increases from 0 to similar to 0.10, in spite of the increase in grain size. However, once the epsilon(VM) exceeds 0.10, the hardness starts to decrease. It is suggested that the role of crystal defect as well as grain size should be considered to better understand the mechanical property of nanocrystalline Ni-20Fe alloy. At small strains (epsilon(VM) <0.10), the increase in hardness is a direct consequence of the high-density crystal defects; while at large strains (epsilon(VM) >0.10), since the crystal defects are saturated, the hardness decreases with further increase in grain size. (C) 2012 Elsevier B.V. All rights reserved.