MOLECULAR-DYNAMIC STUDY OF NANOCRYSTALLINE DEFORMATION OF NICKEL

The study of structural transformations in nanocrystalline nickel, containing <111> and <100> edge boundaries, under the eff ect of deformation was carried out using the method of molecular dynamics. Nanocrystalline nickel was created in the model by crystallization from a liquid state of the computational block in a plate shape of 1.5 – 2.0 nm thickness, containing specifi cally introduced crystal seeds – cylindrical crystalline areas with the fi xed motionless atoms. When creating the computational block, the cylindrical areas with a crystalline structure were rotated to random or predetermined angles around the central axis of cylinders. It was done so that the fi nal crystal grains after crystallization had edge boundaries between each other. Interactions of nickel atoms were described with the help of many-body potential of CleriRosato, constructed in the tight-binding model. Deformation of the compression or tension was set by changing the interatomic distances along a given axis. The main attention was paid to studying the mechanism of plastic deformation with the participation of grain boundaries and triple junctions. The following questions considered: what is the preferably initiator of the plastic shears: surface or boundary; whether there are manifestations of self-organization in this case; whether the dislocations are generated or mechanism of plastic deformation in the case of nanocrystalline structure is mainly due to grain boundary sliding. In the present study, as a result of the computer simulation it was found that the plastic deformation with the grain size of several nm is performed mainly by the grain boundary sliding without the formation of dislocations and intragrain slip. Herewith the grain boundary sliding in some cases accompanies the grain rotation. Displacements of atoms in the plastic deformation process in these materials were formed primarily from free surfaces: at the tension atomic displacements usually were directed from the surface into the polycrystal, at compression, conversely, toward the surface. As a result of the deformation the recrystallization process proceeded in the simulated nanocrystalline Ni more intensively, defects and excess free volume intensively migrated to the interfaces (grain boundaries and free surfaces).

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