Role of dislocations theory.


The expediency of either metals strengthening may be adjusted only after understanding of physical bases of the last ones.

Most of the important properties of metallic materials are determined by their structure, the structure means not only microstructure (grains, the second phase particles), but fine structure - dislocation and disclination structure.. The small changing in the fine structure causes the sharp changing of the properties.

One of the most important structure sensitive properties of advanced metallic materials are mechanical properties.

The last ones determine the plastic strength and fracture under different character of loading.

In the present time it is found that physical nature of the plastic deformation and fracture is described by the dislocation and disclination theories [1-4]. According to the formulated and experimental facts corroborated the last theories it is follows that the dislocations motion is responsible for the deformation. It is possible to increase the plastic retardation of dislocation strength as a result of attacks to the metal structure.

There are four main retardation of dislocation mechanisms[5]:

a) formation of alloying elements atoms jam or segregations or vacansies around the dislocations in the solid solution;

b) the upgrading of the dislocations density result in the intensification of them, moving dislocations when the stress interaction between zone around ones is disturb to the other ones;

c) the formation of the barriers for the moving dislocations as a division surfaces (the different type boundaries) in crystals or the second strengthening phase particles - i.e. the creation of the volumes with different slipping of dislocations crystallography inside of the alloy;

d) the generation of the ordering (with respect to the composition or crystallographical orientations) of atomic configurations; under dislocation motion through the last ones it necessary to expend part of the dislocation energy to the ordering - disordering processes performance result in the dislocations retardation.

It would seem using so wide retardation dislocations methods it is possible to create such structural state in metallic materials wherein the dislocations mobility under high loading will sharply reduced and the plastic strength of increased significantly. But an engineering comprehension of the structural materials strengthening means not only possibility to increase the external loadings without appreciable macroplastic deformation in the given part, but the absence under the designated operation conditions, characterized by the variety of stresses schemes and temperature - rate loading parameters, sudden (premature) destruction. The last ones it is most likely in those cases, when the combined margin of plasticity and toughness metallic materials have lowered, and the relaxation of rised during loading awkward stresses by means of deformation transfer in the neighbour volumes is impeded.


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