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Random effect of grain elongation on cumulative rolling and equal channel angular extrusion strain and strain rate of nanocrystalline materials

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Document pages: 9 pages

Abstract: In the manufacturing process of nanostructured materials, severe plastic deformation technology will produce slender grains. Previous models related to grain size and mechanical properties only considered the equivalent radius, so other methods of measuring grain size were ignored, such as semi minor axis, semi major axis and major axis radius to determine the real grain shape. In this paper, a stochastic model of mechanical properties of nano materials with neglected parameters is proposed. The proposed model was tested with the data of nanocrystalline aluminum samples. The following facts are observed experimentally, and the model also reveals these facts. The grain elongates to the maximum value, and then decreases with further grain refinement due to grain fracture. Yield stress of materialreases with elongation to a maximum and then decreases continuously. The varying approaches of measuring grain radius reveal a common trend of Hall-Petch and Reverse Hall-Petch Relationship but with different critical grain sizes. Materials with high curvature grains have more enhanced yield stress. Reducing strain rates leads to materials with more enhanced yield stress, with critical strain rates values beyond which further reductions do not lead to yield stress enhancement. It can be concluded that, by considering different approaches of measuring grain sizes, reasons for different yield stress for nanomaterials that were observed but could not be explained have been dealt with.

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