Influence of grain size on mechanisms of plastic deformation and yield stress


I. M. Frantsevich Institute for Problems of Materials Science of the NAS of Ukraine, Kyiv
Usp. materialozn. 2020, 1:26-32


In this work, use cellular automata method considers the effect of grain size on the physical yield strength of a polycrystalline materials, that is a stress at which plastic deformation affects the entire cross section of a sample from one edge to another. Three mechanisms of plastic deformation are considered: the initiation of plastic flow from grain to grain by dislocation pile- ups, the occurrence of plastic flow in grains independently from each other under the influence of external stress by dislocations, and intergranular slippage. Using computer simulation, it was shown that at large grain sizes (d > 200 nm), plastic deformation propagates from grain to grain by initiating dislocations pile-ups, since in this case pile-ups are quite powerful and have a large effect on neighboring grains. At average grain sizes (20 nm < d < 200 nm), plastic deformation occurs in the grains independently of each other, and therefore, the external strain exerts a major influence on plastic deformation. And with a further decrease in grain (d < 20 nm), The main mechanism of deformation, which forms the yield strength, is dislocation-free intergranular slippage, since grains of this size have sufficiently large image stresses that prevent large dislocation pile-ups from appearing, and the mass and volume of grains are quite small so that the grain could turn or slip under such external stresses. 

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