A crossover from hardening to softening in nanocrystalline Ni by annealing and rolling |
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| Authors: | Z H Cao P Y Li L Wang Z H Jiang X K Meng |
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| Institution: | 1. National Laboratory of Solid State Microstructures and Department of Material Science and Engineering, Nanjing University, Nanjing, 210093, People??s Republic of China
2. Key Laboratory of Automobile Materials, Department of Materials Science and Engineering, Jilin University, Changchun, 130025, People??s Republic of China
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| Abstract: | Two similar crossover behaviors from hardening to softening were revealed in both annealed and rolled nanocrystalline (NC) Ni by nanoindentation tests, which is totally different from that in coarse-grained samples. X-ray diffraction and transmission electron microscopy results show that the dislocation density continuously decreases with the increment of annealing temperature, whereas it first increases and then decreases with the increased rolling strain. The change of rate sensitivity in annealed NC Ni is different from that of the rolled sample. The crossover from hardening to softening by annealing is attributed to grain-boundary relaxation, while dislocation accumulation and annihilation is responsible for the crossover behavior in rolled NC Ni. |
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