13th International Conference on Fracture June 16–21, 2013, Beijing, China -10- resulting in a substantial reduction of fatigue durability of "coating-substrate" compositions.The combination oflow thickness of themodified surface layer and the ratio of the elastic characteristics compared with more ductile substrate material with high plastic deformations (for instance, in the area of a neck, or plastic tension under cyclic bending) has led to a formation of the system of multiple crackswhose orientation is not always in line with the normal to the direction of the external load.This is a fact that allows us to discuss the thesis of multiple cracking as one of the ways to improve the fatigue durability of "coating-substrate" compositions. 4. Conclusion A study of structure and deformation behavior under static and cyclic tension and alternating bending the specimens of heat resistant 12Cr1MoVsteel subjected to surface layer nanostructuring by zirconium ion beam was performed. It is shown that ultra-dispersed particles of zirconates with the size about 100-150 nm were formed as a result of such treatment in a subsurface layer with a thickness up to several microns. Increase of strength properties by 15 % and decrease elongation before fractureby ~ 19 % is fixed due to thistreatmentat the static tensile. It is found that the formation of the nanostructured surface layer increases the fatigue durability by 2-3 times at cyclic tension tests. The authors associate this with the delay of time the main crack initiationdue tohindering in deformation relief formation which play the key role in propagation of a crack. At cyclic alternating bending the main crack origination in specimens of both types happens at almost equal numbers of cycles that is associated with the periodic occurrence in the surface layer of tensile and compressive stresses. However, at a subsequent stage the growth rate of the main crack is differing approximatelyin 2 times because of the nanostructured surface layer hinders microcracks origin on the grain boundaries of the substrate. This result is consistent with data of distinction comparison for both fatigue crack growth rate at the cyclic tensile and bending. For the second case, the growth rate is several times less. The influence of multiple cracking on improving fatigue durability of specimens under study is discussed. It is shown that in the area of the main crack (predominantly under cyclic tensile) the finite length microcracks whose orientation does not always coincide with the direction of normal to the axis of the applied load are formed. This fact may be the manifestation of the effect of channeling plastic shears in the substrate material. References [1] Shaniavskii А.А. Safe fatiguefracture of elements aviastructures: Synergetics in engineering applications /–Ufa: Izdatel’stvoUGNTU, 2003. – 802 p. [2] Didenko А.N., Sharkeev Yu.P., Kozlov E.V., Ryabchikov А.I. Effects of long-range interaction in ion-implanted metal materials / – Tomsk: Izdatel’stvoNTL, 2004. – 328 p. [3] PaninV.Е., Sergeev V.P., PaninA.V.Nanostructuringofsurface layers of structural materials and deposition of nanostructured coatings / – Tomsk: Polytechnic University, 2008. – 286 p. [4] PaninV.Е., EgorushkinV.E., PaninA.V.The effect of channeling plastic shears and nonlinear waves of localized plastic deformation and fracture// Phys. Mesomech. –2010. –Т. 13. – N5. – P. 7-26.
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