Study Of The Mechanical Behavior And Deformation Mechanisms Of Nanocrystalline Metallic Silver

The tensile and compression experiment on bulk nanocrystalline Ag prepared by IGC method was carried on MT810 with different grain sizes and Zwick 10TN2S Machine at different strain rates under normal temperature respectively. The stain rate sensitivity m was found to be 0.025, which was extremely lower than the ordinary values. Also the work hardening exponent is very low. Under the careful retrospection and analysis on the previous and recent experiments about mechanical behavior of nanocrystalline metals performed by almost main investigators, the dislocation and atomic diffusion is believed to contribute hardly to the deformation of nanocrystalline alloy, and a model based on thermal activation process was applied to fit the experimental data of nanocrystalline Ag. The apparent activation volume calculated by the model is about 2500A3, which was ten times larger than that of usual amorphous alloy and was at the same range of the amorphous polymer.The model shows the main deformation mechanism of nanocrystalline Ag is grain boundary sliding, which in some extent declares the similar forms of equation with amorphous alloys. With the ananlysis to the HREM of nanocrystalline Ag, the discrepancy of the apparent activation volume between the nanocrystalline Ag and amorphous alloys is interpreted by the loss of atoms participating in grain boundary sliding without enough reconstruction by the movement of atoms under the low temperature.To explain the inverse Hall-Petch relation in nanocrystalline metals, a geometric model is made, which assumes that the grains are spherical crystals, and the thick of grain boundary is considerable compared with the microcrystalline metals. This model also throws a light on the ability of getting high strength of nanocrystalline metals through amorphous metals' crystallization.