PSI - Issue 30

L.V. Moskvitina et al. / Procedia Structural Integrity 30 (2020) 100–104 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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Fig. 2. Structures of deformation and destruction in the area of stable growth of the fatigue crack, TEM: (a) strip structures in the deformed grain; (b) surface of destruction on strip structures; (c) a cellular structure in the deformed grains; (d) surface of destruction on a cellular structure. By alternating polish and etching with 15% nitric acid in ethanol and 5% picric acid in ethanol, the structures of deformation were revealed on aged ferrite. In Fig. 2c shows a disoriented cellular structure of deformation on the aged ferrite. The «shagreen» surfa ce of grains is conditioned by dispersed inclusions. The walls of deformation structures are presented by interlaced system of distributions. According to classification based on the work (Panin 1990) a cellular structure refers to non-disoriented substructures of the dislocation type. The strip structure refers to disoriented dislocation-disclination formations. The fatigue destruction in the cellular structure takes place by splitting along slip planes with rare crack stops forming intermittent fatigue grooves (Fig. 2d). As noted in the data of Troshchenko et al.(1978), such facets are characteristic for the development of destruction on the ageing area. In the fatigue destruction at positive temperatures, hardening of the ferrite by the secondary phase inhibits the development of cracks (Ivanova et al. 1975). The formation of facets of one-time crack on aged ferrite is apparently conditioned by the cooling of metal at low environment temperature. The low circular character of destruction influenced by high intensity of alternating loading is caused by a small share of the fatigue zone, an abrupt and not extracted transition to the area of accelerated development of crack, development of the crack by splitting along strip and cellular structures, due to the irregularity of fatigue grooves (Ivanova et al. 1975; Krasovsky 1980; Gulyaev et al. 1973). 3.3. Fragmentation of structure at accelerated development of crack. The macroscopic structure of the fracture shows that the tipper M-200 halted motion only after the final catastrophic destruction of the rim. It means that the accelerated development of the crack proceeded at temperature 40 0 С under the influence of alternating tensions of high intensity. At optical zoom, it is evident that in the