Microstructure evolution and mechanical properties of nanocrystalline Ni–30Fe alloy

The microstructure evolution and hardness of nanocrystalline Ni–30 wt% Fe alloys during cold rolling are investigated by X-ray diffraction and hardness measurement. We report the Ni–30Fe alloy reaches a maximum hardness at an equivalent strain of about 0.05. This strain hardening behavior of the Ni–30Fe alloy differs from that of pure nickel, due to the fact the Ni–30Fe alloy has lower stacking fault energy. When the samples are further deformed, strain softening takes place. It is suggested that crystal defects and grain size are significant in exploring the hardness of nanocrystalline Ni–30Fe alloys. At smaller strains within 0.05, the increase in hardness is a direct result of the high density of crystalline defects; while at larger strains above 0.05, due to the finite even reduced crystalline defects, the hardness starts to decrease with increasing grain size.