13th International Conference on Fracture June 16–21, 2013, Beijing, China -8- а) b) Figure 4. Optical micrographs to illustrate strain induced reliefonthe surfaceofspecimens: а) without treatment; b) withnanostructured surface layer 3. Discussion of results The first effect of the surface layer nanostructuring which is to be stressed is the noticeable increase of flowstress with a ratherlow decrease of ductility. Traditionally, ion beam treatment is accompanied by the formation of a layer with thickness up to 0.1 micron, whereas under the treatment used the thickness of modified layer is estimated as 2 µm (according to the data of optical profilometry of the cracked layer) up to 10 µm (according to data of the scanning electron microscopy at observation of the fracturesurface after fatigue fracture).In doing so, presence of multiple cracksin the modified layerin the vicinity of neck exerts no significant impact on the reduction of plasticity due to the small thickness of the modified layer,as well as realization of multiple cracking. As a result, none of the cracks becomes the main oneand plastic deformation of the composition is determined mostlyby the development of plastic flow in the ductile material of the substrate. The following key result is associated with notable changein the character of the localized plastic deformation development in the subsurface.It is shown that the layer to have the 1.5 times increased hardness and thickness of several microns can significantly change the pattern of the deformation relief formed. At low strain of the substrate (for example, at static tension out the neck area) deformation relief on the surface almost is not formed while in the region of intensive development of plastic deformation the size of strain induced relief elements is noticeably bigger than that in specimens without the treatment. This result is consistent with data on the cyclic bending tests
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